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This executive summary reviews the topics covered in this PDQ summary on the genetics of prostate cancer, with hyperlinks to detailed sections below that describe the evidence on each topic.
A genetic contribution to prostate cancer risk has been documented, and knowledge about the molecular genetics of the disease is increasing. Clinical management based on knowledge of inherited pathogenic variants is emerging. Factors suggestive of a genetic contribution to prostate cancer include the following: 1) multiple affected first-degree relatives (FDRs) with prostate cancer, including three successive generations with prostate cancer in the maternal or paternal lineage; 2) early-onset prostate cancer (age =55 years); and 3) prostate cancer with a family history of other cancers (e.g., breast, ovarian, pancreatic).
Several genes and chromosomal regions have been found to be associated with prostate cancer in various linkage analyses, case-control studies, genome-wide association studies (GWAS), and admixture mapping studies. Pathogenic variants in genes of high and moderate penetrance, such as BRCA1, BRCA2, the mismatch repair genes, and HOXB13 confer modest to high lifetime risk of prostate cancer. Some, such as BRCA2, have emerging clinical relevance in the treatment and screening for prostate cancer. In addition, GWAS have identified more than 100 SNPs associated with the development of prostate cancer, but the clinical utility of these findings remains uncertain. Studies are ongoing to assess whether combinations of these SNPs may have clinical relevance in identifying individuals at increased risk of the disease. Studies analyzing the association between variants and aggressive disease are also ongoing.
Information is limited about the efficacy of commonly available screening tests such as the digital rectal exam and serum prostate-specific antigen (PSA) levels in men genetically predisposed to developing prostate cancer. Initial reports of targeted PSA screening of carriers of BRCA pathogenic variants has yielded a higher proportion of aggressive disease. On the basis of the available data, most professional societies and organizations recommend that high-risk men engage in shared decision-making with their health care providers and develop individualized plans for prostate cancer screening based on their risk factors. For example, some experts suggest initiating prostate cancer screening at age 45 years in carriers of BRCA2 pathogenic variants and consideration of screening in BRCA1 carriers. Inherited variants may influence treatment decisions, particularly for males with pathogenic variants in DNA repair genes. Studies have reported improved response rates to poly (ADP-ribose) polymerase (PARP) inhibition among males with metastatic, castrate-resistant prostate cancer carrying germline pathogenic variants in BRCA2 and other DNA repair genes.
Psychosocial research in men at increased hereditary risk of prostate cancer has focused on risk perception, interest in genetic testing, and screening behaviors. Study conclusions vary regarding whether FDRs of prostate cancer patients accurately estimate their prostate cancer risk, with some studies reporting that men with a family history of prostate cancer consider their risk to be the same as or less than that of the average man. Factors such as being married and the confusion between benign prostatic hyperplasia and prostate cancer have been found to influence perceived risk of prostate cancer. Studies conducted before the availability of genetic testing for prostate cancer susceptibility showed that factors found to positively influence men's hypothetical interest in genetic testing included the advice of their primary care physician, a combination of the emotional distress and concern about prostate cancer treatment effects, and having children. Several small studies have examined the behavioral correlates of prostate cancer screening at average and increased prostate cancer risk based on family history; in general, results appear contradictory regarding whether men with a family history are more likely to be screened than those not at risk and whether the screening is appropriate for their risk status. Research is ongoing to better understand and address psychosocial and behavioral issues in high-risk families.
Many of the medical and scientific terms used in this summary are found in the NCI Dictionary of Genetics Terms. When a linked term is clicked, the definition will appear in a separate window.
Many of the genes described in this summary are found in the Online Mendelian Inheritance in Man (OMIM) database. When OMIM appears after a gene name or the name of a condition, click on OMIM for a link to more information.
A concerted effort is being made within the genetics community to shift terminology used to describe genetic variation. The shift is to use the term "variant" rather than the term "mutation" to describe a difference that exists between the person or group being studied and the reference sequence. Variants can then be further classified as benign (harmless), likely benign, of uncertain significance, likely pathogenic, or pathogenic (disease causing). Throughout this summary, we will use the term pathogenic variant to describe a disease-causing mutation. Refer to the Cancer Genetics Overview summary for more information about variant classification.
The public health burden of prostate cancer is substantial. A total of 164,690 new cases of prostate cancer and 29,430 deaths from the disease are anticipated in the United States in 2018, making it the most frequent nondermatologic cancer among U.S. males. A man's lifetime risk of prostate cancer is one in nine. Prostate cancer is the second leading cause of cancer death in men, exceeded only by lung cancer.
Some men with prostate cancer remain asymptomatic and die from unrelated causes rather than as a result of the cancer itself. This may be due to the advanced age of many men at the time of diagnosis, slow tumor growth, or response to therapy. The estimated number of men with latent prostate carcinoma (i.e., prostate cancer that is present in the prostate gland but never detected or diagnosed during a patient's life) is greater than the number of men with clinically detected disease. A better understanding is needed of the genetic and biologic mechanisms that determine why some prostate carcinomas remain clinically silent, while others cause serious, even life-threatening illness.
Prostate cancer exhibits tremendous differences in incidence among populations worldwide; the ratio of countries with high and low rates of prostate cancer ranges from 60-fold to 100-fold. Asian men typically have a very low incidence of prostate cancer, with age-adjusted incidence rates ranging from 2 to 10 cases per 100,000 men. Higher incidence rates are generally observed in northern European countries. African American men, however, have the highest incidence of prostate cancer in the world; within the United States, African American men have a 60% higher incidence rate than white men. African American men have been reported to have more than twice the rate of prostate cancer-specific death compared with non-Hispanic white men. Differences in race-specific prostate cancer survival estimates may be narrowing over time.
These differences may be due to the interplay of genetic, environmental, and social influences (such as access to health care), which may affect the development and progression of the disease. Differences in screening practices have also had a substantial influence on prostate cancer incidence, by permitting prostate cancer to be diagnosed in some patients before symptoms develop or before abnormalities on physical examination are detectable. An analysis of population-based data from Sweden suggested that a diagnosis of prostate cancer in one brother leads to an early diagnosis in a second brother using prostate-specific antigen (PSA) screening. This may account for an increase in prostate cancer diagnosed in younger men that was evident in nationwide incidence data. A genetic contribution to prostate cancer risk has been documented, and there is increasing knowledge of the molecular genetics of the disease, although much of what is known is not yet clinically actionable. Malignant transformation of prostate epithelial cells and progression of prostate carcinoma are likely to result from a complex series of initiation and promotional events under both genetic and environmental influences.
Risk Factors for Prostate Cancer
The three most important recognized risk factors for prostate cancer in the United States are:
Age is an important risk factor for prostate cancer. Prostate cancer is rarely seen in men younger than 40 years; the incidence rises rapidly with each decade thereafter. For example, the probability of being diagnosed with prostate cancer is 1 in 403 for men 49 years or younger, 1 in 58 for men aged 50 through 59 years, 1 in 21 for men aged 60 through 69 years, and 1 in 12 for men aged 70 years and older, with an overall lifetime risk of developing prostate cancer of 1 in 9.
Approximately 10% of prostate cancer cases are diagnosed in men younger than 56 years and represent early-onset prostate cancer. Data from the Surveillance, Epidemiology, and End Results (SEER) Program show that early-onset prostate cancer is increasing, and there is evidence that some cases may be more aggressive. Because early-onset cancers may result from germline pathogenic variants, young men with prostate cancer are being extensively studied with the goal of identifying prostate cancer susceptibility genes.
The risk of developing and dying from prostate cancer is dramatically higher among blacks, is of intermediate levels among whites, and is lowest among native Japanese.[10,11] Conflicting data have been published regarding the etiology of these outcomes, but some evidence is available that access to health care may play a role in disease outcomes.
Family history of prostate cancer
Prostate cancer is highly heritable; the inherited risk of prostate cancer has been estimated to be as high as 60%. As with breast and colon cancer, familial clustering of prostate cancer has been reported frequently.[14,15,16,17,18] From 5% to 10% of prostate cancer cases are believed to be primarily caused by high-risk inherited genetic factors or prostate cancer susceptibility genes. Results from several large case-control studies and cohort studies representing various populations suggest that family history is a major risk factor in prostate cancer.[15,19,20] A family history of a brother or father with prostate cancer increases the risk of prostate cancer, and the risk is inversely related to the age of the affected relative.[16,17,18,19,20] However, at least some familial aggregation is due to increased prostate cancer screening in families thought to be at high risk.
Although some of the prostate cancer studies examining risks associated with family history have used hospital-based series, several studies described population-based series.[22,23,24] The latter are thought to provide information that is more generalizable. A meta-analysis of 33 epidemiologic case-control and cohort-based studies has provided more detailed information regarding risk ratios related to family history of prostate cancer. Risk appeared to be greater for men with affected brothers than for men with affected fathers in this meta-analysis. Although the reason for this difference in risk is unknown, possible hypotheses have included X-linked or recessive inheritance. In addition, risk increased with increasing numbers of affected close relatives. Risk also increased when a first-degree relative (FDR) was diagnosed with prostate cancer before age 65 years. (Refer to Table 1 for a summary of the relative risks [RRs] related to a family history of prostate cancer.)
Among the many data sources included in this meta-analysis, those from the Swedish population-based Family-Cancer Database warrant special comment. These data were derived from a resource that contained more than 11.8 million individuals, among whom there were 26,651 men with medically verified prostate cancer, of which 5,623 were familial cases. The size of this data set, with its nearly complete ascertainment of the entire Swedish population and objective verification of cancer diagnoses, should yield risk estimates that are both accurate and free of bias. When the familial age-specific hazard ratios (HRs) for prostate cancer diagnosis and mortality were computed, as expected, the HR for prostate cancer diagnosis increased with more family history. Specifically, HRs for prostate cancer were 2.12 (95% CI, 2.05-2.20) with an affected father only, 2.96 (95% CI, 2.80-3.13) with an affected brother only, and 8.51 (95% CI, 6.13-11.80) with a father and two brothers affected. The highest HR, 17.74 (95% CI, 12.26-25.67), was seen in men with three brothers diagnosed with prostate cancer. The HRs were even higher when the affected relative was diagnosed with prostate cancer before age 55 years.
A separate analysis of this Swedish database reported that the cumulative (absolute) risks of prostate cancer among men in families with two or more affected cases were 5% by age 60 years, 15% by age 70 years, and 30% by age 80 years, compared with 0.45%, 3%, and 10%, respectively, by the same ages in the general population. The risks were even higher when the affected father was diagnosed before age 70 years. The corresponding familial population attributable fractions (PAFs) were 8.9%, 1.8%, and 1.0% for the same three age groups, respectively, yielding a total PAF of 11.6% (i.e., approximately 11.6% of all prostate cancers in Sweden can be accounted for on the basis of familial history of the disease).
The risk of prostate cancer may also increase in men who have a family history of breast cancer. Approximately 9.6% of the Iowa cohort had a family history of breast and/or ovarian cancer in a mother or sister at baseline, and this was positively associated with prostate cancer risk (age-adjusted RR, 1.7; 95% CI, 1.0-3.0; multivariate RR, 1.7; 95% CI, 0.9-3.2). Men with a family history of both prostate and breast/ovarian cancer were also at increased risk of prostate cancer (RR, 5.8; 95% CI, 2.4-14.0). Analysis of data from the Women's Health Initiative also showed that a family history of prostate cancer was associated with an increase in the risk of postmenopausal breast cancer (adjusted HR, 1.14; 95% CI, 1.02-1.26). Further analyses showed that breast cancer risk was associated with a family history of both breast and prostate cancers; the risk was higher in black women than in white women. Other studies, however, did not find an association between family history of female breast cancer and risk of prostate cancer.[22,29] A family history of prostate cancer also increases the risk of breast cancer among female relatives. The association between prostate cancer and breast cancer in the same family may be explained, in part, by the increased risk of prostate cancer among men with BRCA1/BRCA2pathogenic variants in the setting of hereditary breast/ovarian cancer or early-onset prostate cancer.[31,32,33,34] (Refer to the BRCA1 and BRCA2 section of this summary for more information.)
Prostate cancer clusters with particular intensity in some families. Highly penetrant genetic variants are thought to be associated with prostate cancer risk in these families. (Refer to the Linkage Analyses section of this summary for more information.) Members of such families may benefit from genetic counseling. Emerging recommendations and guidelines for genetic counseling referrals are based on prostate cancer age at diagnosis and specific family cancer history patterns.[35,36] Individuals meeting the following criteria may warrant referral for genetic consultation:[35,36,37,38]
Family history has been shown to be a risk factor for men of different races and ethnicities. In a population-based case-control study of prostate cancer among African Americans, whites, and Asian Americans in the United States (Los Angeles, San Francisco, and Hawaii) and Canada (Vancouver and Toronto), 5% of controls and 13% of all cases reported a father, brother, or son with prostate cancer. These prevalence estimates were somewhat lower among Asian Americans than among African Americans or whites. A positive family history was associated with a twofold to threefold increase in RR in each of the three ethnic groups. The overall odds ratio associated with a family history of prostate cancer was 2.5 (95% CI, 1.9-3.3) with adjustment for age and ethnicity.
There is little evidence that family history alone is associated with inferior clinical outcomes. In a cohort of 7,690 men in Germany who were undergoing radical prostatectomy for localized prostate cancer, family history had no bearing on prostate cancer-specific survival.
Other potential modifiers of prostate cancer risk
Endogenous hormones, including both androgens and estrogens, likely influence prostate carcinogenesis. It has been widely reported that eunuchs and other individuals with castrate levels of testosterone before puberty do not develop prostate cancer. Some investigators have considered the potential role of genetic variation in androgen biosynthesis and metabolism in prostate cancer risk, including the potential role of the androgen receptor (AR) CAG repeat length in exon 1. This modulates AR activity, which may influence prostate cancer risk. For example, a meta-analysis reported that AR CAG repeat length greater than or equal to 20 repeats conferred a protective effect for prostate cancer in subsets of men.
(Refer to the PDQ summary on Prostate Cancer Prevention for more information about nongenetic modifiers of prostate cancer risk in the general population.)
The SEER Cancer Registries assessed the risk of developing a second primary cancer in 292,029 men diagnosed with prostate cancer between 1973 and 2000. Excluding subsequent prostate cancer and adjusting for the risk of death from other causes, the cumulative incidence of a second primary cancer among all patients was 15.2% at 25 years (95% CI, 15.0%-15.4%). There was a significant risk of new malignancies (all cancers combined) among men diagnosed before age 50 years, no excess or deficit in cancer risk in men aged 50 to 59 years, and a deficit in cancer risk in all older age groups. The authors suggested that this deficit may be attributable to decreased cancer surveillance in an elderly population. Excess risks of second primary cancers included cancers of the small intestine, soft tissue, bladder, thyroid, and thymus; and melanoma. Prostate cancer diagnosed in patients aged 50 years or younger was associated with an excess risk of pancreatic cancer.
A review of more than 441,000 men diagnosed with prostate cancer between 1992 and 2010 demonstrated similar findings, with an overall reduction in the risk of being diagnosed with a second primary cancer. This study also examined the risk of second primary cancers in 44,310 men (10%) by treatment modality for localized cancer. The study suggested that men who received radiation therapy had increases in bladder (standardized incidence ratio [SIR], 1.42) and rectal cancer risk (SIR, 1.70) compared with those who did not receive radiation therapy (SIRbladder, 0.76; SIRrectal, 0.74).
The underlying etiology of developing a second primary cancer after prostate cancer may be related to various factors, including treatment modality. More than 50% of the small intestine tumors were carcinoid malignancies, suggesting possible hormonal influences. The excess of pancreatic cancer may be due to pathogenic variants in BRCA2, which predisposes to both. The risk of melanoma was most pronounced in the first year of follow-up after diagnosis, raising the possibility that this is the result of increased screening and surveillance.
One Swedish study using the nationwide Swedish Family Cancer Database assessed the role of family history in the risk of a second primary cancer after prostate cancer. Of 18,207 men with prostate cancer, 560 developed a second primary malignancy. Of those, the RR was increased for colorectal, kidney, bladder, and squamous cell skin cancers. Having a paternal family history of prostate cancer was associated with an increased risk of bladder cancer, myeloma, and squamous cell skin cancer. Among prostate cancer probands, those with a family history of colorectal cancer, bladder cancer, or chronic lymphoid leukemia were at increased risk of that specific cancer as a second primary cancer.
Data are emerging that prostate cancer patients who have at least one additional primary malignancy disproportionately harbor pathogenic variants in known cancer-predisposing genes, such as BRCA2 and MLH1.
Risk of Other Cancers in Multiple-Case Families
Several reports have suggested an elevated risk of various other cancers among relatives within multiple-case prostate cancer families, but none of these associations have been established definitively.[49,50,51]
In a population-based Finnish study of 202 multiple-case prostate cancer families, no excess risk of all cancers combined (other than prostate cancer) was detected in 5,523 family members. Female family members had a marginal excess of gastric cancer (SIR, 1.9; 95% CI, 1.0-3.2). No difference in familial cancer risk was observed when families affected by clinically aggressive prostate cancers were compared with those having nonaggressive prostate cancer. These data suggest that familial prostate cancer is a cancer site-specific disorder.
Inheritance of Prostate Cancer Risk
Many types of epidemiologic studies (case-control, cohort, twin, family) strongly suggest that prostate cancer susceptibility genes exist in the population. Analysis of longer follow-up of the monozygotic (MZ) and dizygotic (DZ) twin pairs in Scandinavia concluded that 58% (95% CI, 52%-63%) of prostate cancer risk may be accounted for by heritable factors. Additionally, among affected MZ and DZ pairs, the time to diagnosis in the second twin was shortest in MZ twins (mean, 3.8 years in MZ twins vs. 6.5 years in DZ twins). This is in agreement with a previous U.S. study that showed a concordance of 7.1% between DZ twin pairs and a 27% concordance between MZ twin pairs. The first segregation analysis was performed in 1992 using families from 740 consecutive probands who had radical prostatectomies between 1982 and 1989. The study results suggested that familial clustering of disease among men with early-onset prostate cancer was best explained by the presence of a rare (frequency of 0.003) autosomal dominant, highly penetrant allele(s). Hereditary prostate cancer susceptibility genes were predicted to account for almost half of early-onset disease (age 55 years or younger). In addition, early-onset disease has been further supported to have a strong genetic component from the study of common variants associated with disease onset before age 55 years.
Subsequent segregation analyses generally agreed with the conclusions but differed in the details regarding frequency, penetrance, and mode of inheritance.[55,56,57] A study of 4,288 men who underwent radical prostatectomy between 1966 and 1995 found that the best fitting genetic model of inheritance was the presence of a rare, autosomal dominant susceptibility gene (frequency of 0.06). In this study, the lifetime risk in carriers was estimated to be 89% by age 85 years and 3.9% for noncarriers. This study also suggested the presence of genetic heterogeneity, as the model did not reliably predict prostate cancer risk in FDRs of probands who were diagnosed at age 70 years or older. More recent segregation analyses have concluded that there are multiple genes associated with prostate cancer [58,59,60,61] in a pattern similar to other adult-onset hereditary cancer syndromes, such as those involving the breast, ovary, colorectum, kidney, and melanoma. In addition, a segregation analysis of 1,546 families from Finland found evidence for mendelian recessive inheritance. Results showed that individuals carrying the risk allele were diagnosed with prostate cancer at younger ages (<66 years) than noncarriers. This is the first segregation analysis to show a recessive mode of inheritance.
Various research methods have been employed to uncover the landscape of genetic variation associated with prostate cancer. Specific methodologies inform of unique phenotypes or inheritance patterns. The sections below describe prostate cancer research utilizing various methods to highlight their role in uncovering the genetic basis of prostate cancer. In an effort to identify disease susceptibility genes, linkage studies are typically performed on high-risk extended families in which multiple cases of a particular disease have occurred. Typically, pathogenic variants identified through linkage analyses are rare in the population, are moderately to highly penetrant in families, and have large (e.g., relative risk >2.0) effect sizes. The clinical role of pathogenic variants that are identified in linkage studies is a clearer one, establishing precedent for genetic testing for cancer with genes such as BRCA1 and BRCA2. (Refer to the BRCA1 and BRCA2 section in the Genes With Potential Clinical Relevance in Prostate Cancer Risk section of this summary for more information about these genes.) Genome-wide association studies (GWAS) are another methodology used to identify candidate loci associated with prostate cancer. Genetic variants identified from GWAS typically are common in the population and have low to modest effect sizes for prostate cancer risk. The clinical role of markers identified from GWAS is an active area of investigation. Case-control studies are useful in validating the findings of linkage studies and GWAS as well as for studying candidate gene alterations for association with prostate cancer risk, although the clinical role of findings from case-control studies needs to be further defined.
Introduction to linkage analyses
The recognition that prostate cancer clusters within families has led many investigators to collect multiple-case families with the goal of localizing prostate cancer susceptibility genes through linkage studies.
Linkage studies are typically performed on high-risk kindreds in whom multiple cases of a particular disease have occurred in an effort to identify disease susceptibility genes. Linkage analysis statistically compares the genotypes between affected and unaffected individuals and looks for evidence that known genetic markers are inherited along with the disease trait. If such evidence is found (linkage), it provides statistical data that the chromosomal region near the marker also harbors a disease susceptibility gene. Once a genomic region of interest has been identified through linkage analysis, additional studies are required to prove that there truly is a susceptibility gene at that position. Linkage analysis is affected by the following:
Furthermore, because a standard definition of hereditary prostate cancer has not been accepted, prostate cancer linkage studies have not used consistent criteria for enrollment. One criterion that has been proposed is the Hopkins Criteria, which provides a working definition of hereditary prostate cancer families. Using the Hopkins Criteria, kindreds with prostate cancer need to fulfill only one of following criteria to be considered to have hereditary prostate cancer:
Using these criteria, surgical series have reported that approximately 3% to 5% of men will be from a family with hereditary prostate cancer.[2,3]
An additional issue in linkage studies is the high background rate of sporadic prostate cancer in the context of family studies. Because a man's lifetime risk of prostate cancer is one in nine, it is possible that families under study have men with both inherited and sporadic prostate cancer. Thus, men who do not inherit the prostate cancer susceptibility gene that is segregating in their family may still develop prostate cancer. There are no clinical or pathological features of prostate cancer that will allow differentiation between inherited and sporadic forms of the disease, although current advances in the understanding of molecular phenotypes of prostate cancer may be informative in identifying inherited prostate cancer. Similarly, there are limited data regarding the clinical phenotype or natural history of prostate cancer associated with specific candidate loci. Measurement of the serum prostate-specific antigen (PSA) has been used inconsistently in evaluating families used in linkage analysis studies of prostate cancer. In linkage studies, the definition of an affected man can be biased by the use of serum PSA screening as the rates of prostate cancer in families will differ between screened and unscreened families.
One way to address inconsistencies between linkage studies is to require inclusion criteria that define clinically significant disease (e.g., Gleason score =7, PSA =20 ng/mL) in an affected man.[5,6,7] This approach attempts to define a homogeneous set of cases/families to increase the likelihood of identifying a linkage signal. It also prevents the inclusion of cases that may be considered clinically insignificant that were identified by screening in families.
Investigators have also incorporated clinical parameters into linkage analyses with the goal of identifying genes that may influence disease severity.[8,9] This type of approach, however, has not yet led to the identification of consistent linkage signals across datasets.[10,11]
Susceptibility loci identified in linkage analyses
Table 2 summarizes the proposed prostate cancer susceptibility loci identified in families with multiple prostate cancer-affected individuals. Conflicting evidence exists regarding the linkage to some of the loci described above. Data on the proposed phenotype associated with each locus are also limited, and the strength of repeated studies is needed to firmly establish these associations. Evidence suggests that many of these prostate cancer loci account for disease in a small subset of families, which is consistent with the concept that prostate cancer exhibits locus heterogeneity.
Other genetic loci discovered by linkage analysis
Genome-wide linkage studies of families with prostate cancer have identified several other loci that may harbor prostate cancer susceptibility genes, emphasizing the underlying complexity and genetic heterogeneity of this cancer. The following chromosomal regions have been found to be associated with prostate cancer in more than one study or clinical cohort with a statistically significant (=2) logarithm of the odds (LOD) score, heterogeneity LOD (HLOD) score, or summary LOD score:
The chromosomal region 19q has also been found to be associated with prostate cancer, although specific LOD scores have not been described.[8,11,95]
Linkage analyses in various familial phenotypes
Linkage studies have also been performed in specific populations or with specific clinical parameters to identify population-specific susceptibility genes or genes influencing disease phenotypes.
Linkage analysis in African American families
The African American Hereditary Prostate Cancer study conducted a genome-wide linkage study of 77 families with four or more affected men. Multipoint HLOD scores of 1.3 to less than 2.0 were observed using markers that map to 11q22, 17p11, and Xq21. Analysis of the 16 families with more than six men with prostate cancer provided evidence for two additional loci: 2p21 (multipoint HLOD score = 1.08) and 22q12 (multipoint HLOD score = 0.91).[92,99] A smaller linkage study that included 15 African American hereditary prostate cancer families from the southeastern and southcentral Louisiana region identified suggestive linkage for prostate cancer at 2p16 (HLOD = 1.97) and 12q24 (HLOD = 2.21) using a 6,000 single nucleotide polymorphism (SNP) platform. Further study including a larger number of African American families is needed to confirm these findings.
Linkage analysis in families with aggressive prostate cancer
In an effort to identify loci contributing to prostate cancer aggressiveness, linkage analysis was performed in families with one or more of the following: Gleason grade 7 or higher, PSA of 20 ng/mL or higher, regional or distant cancer stage at diagnosis, or death from metastatic prostate cancer before age 65 years. One hundred twenty-three families with two or more affected family members with aggressive prostate cancer were studied. Suggestive linkage was found at chromosome 22q11 (HLOD score = 2.18) and 22q12.3-q13.1 (HLOD score = 1.90). These findings suggest that using a clinically defined phenotype may facilitate finding prostate cancer susceptibility genes. A fine-mapping study of 14 extended high-risk prostate cancer families has subsequently narrowed the genomic region of interest to an 880-kb region at 22q12.3. An analysis of high-risk pedigrees from Utah provides an overview of this strategy. A linkage analysis utilizing a higher resolution marker set of 6,000 SNPs was performed among 348 families from the International Consortium for Prostate Cancer Genetics with aggressive prostate cancer. Aggressive disease was defined as Gleason score 7 or higher, invasion into seminal vesicles or extracapsular extension, pretreatment PSA level of 20 ng/mL or higher, or death from prostate cancer. The region with strongest evidence of linkage among aggressive prostate cancer families was 8q24 with LOD scores of 3.09-3.17. Additional regions of linkage included with LOD scores of 2 or higher included 1q43, 2q35, and 12q24.31. No candidate genes have been identified.
Linkage analysis in families with multiple cancers
In light of the multiple prostate cancer susceptibility loci and disease heterogeneity, another approach has been to stratify families based on other cancers, given that many cancer susceptibility genes are pleiotropic. A genome-wide linkage study was conducted to identify a susceptibility locus that may account for both prostate cancer and kidney cancer in families. Analysis of 15 families with evidence of hereditary prostate cancer and one or more cases of kidney cancer (pathologically confirmed) in a man with prostate cancer or in a first-degree relative of a man with prostate cancer revealed suggestive linkage with markers that mapped to an 8 cM region of chromosome 11p11.2-q12.2. This observation awaits confirmation. Another genome-wide linkage study was conducted in 96 hereditary prostate cancer families with one or more first-degree relatives with colon cancer. Evidence for linkage in all families was found in several regions, including 11q25, 15q14, and 18q21. In families with two or more cases of colon cancer, linkage was also observed at 1q31, 11q14, and 15q11-14.
Summary of prostate cancer linkage studies
Linkage to chromosome 17q21-22 and subsequent fine-mapping and targeted sequencing have identified recurrent pathogenic variants in the HOXB13 gene that account for a fraction of hereditary prostate cancer, particularly early-onset prostate cancer. Multiple studies have confirmed the association between the G84E pathogenic variant in HOXB13 and prostate cancer risk. (Refer to the HOXB13 section of this summary for more information.) The clinical utility of testing for HOXB13 pathogenic variants has not yet been defined, but studies are ongoing to define the clinical role. For example, a study evaluated 948 unselected men scheduled for prostate biopsy. The G84E pathogenic variant was found in three men (0.3%) who had prostate cancer detected on biopsy, although none of the 301 men who had a family history of prostate cancer carried the variant. Furthermore, many linkage studies have mapped several prostate cancer susceptibility loci (Table 2), although the genetic alterations contributing to hereditary prostate cancer from these loci have not been consistently reproduced. With the evolution of high-throughput sequencing technologies, there will likely be additional moderately to highly penetrant genetic variants identified to account for subsets of hereditary prostate cancer families.
A case-control study involves evaluating factors of interest for association to a condition. The design involves investigation of cases with a condition of interest, such as a specific disease or genetic variant, compared with a control sample without that condition, but often with other similar characteristics (i.e., age, gender, and ethnicity). Limitations of case-control design with regard to identifying genetic factors include the following:[117,118]
Additionally, identified associations may not always be valid, but they could represent a random association and, therefore, warrant validation studies.[117,118]
Genes interrogated in case-control studies
Androgen receptor (AR) gene variants have been examined in relation to both prostate cancer risk and disease progression. The AR is expressed during all stages of prostate carcinogenesis. One study demonstrated that men with hereditary prostate cancer who underwent radical prostatectomy had a higher percentage of prostate cancer cells exhibiting expression of the AR and a lower percentage of cancer cells expressing estrogen receptor alpha than did men with sporadic prostate cancer. The authors suggest that a specific pattern of hormone receptor expression may be associated with hereditary predisposition to prostate cancer.
Altered activity of the AR caused by inherited variants of the AR gene may influence risk of prostate cancer. The length of the polymorphic trinucleotide CAG and GGN microsatellite repeats in exon 1 of the AR gene (located on the X chromosome) have been associated with the risk of prostate cancer.[122,123] Some studies have suggested an inverse association between CAG repeat length and prostate cancer risk, and a direct association between GGN repeat length and risk of prostate cancer; however, the evidence is inconsistent.[120,122,123,124,125,126,127,128,129,130,131,132] A meta-analysis of 19 case-control studies demonstrated a statistically significant association between both short CAG length (odds ratio [OR], 1.2; 95% confidence interval [CI], 1.1-1.3) and short GGN length (OR, 1.3; 95% CI, 1.1-1.6) and prostate cancer; however, the absolute difference in number of repeats between cases and controls is less than one, leading the investigators to question whether these small, statistically significant differences are biologically meaningful. Subsequently, the large multiethnic cohort study of 2,036 incident prostate cancer cases and 2,160 ethnically matched controls failed to confirm a statistically significant association (OR, 1.02; P = .11) between CAG repeat size and prostate cancer. A study of 1,461 Swedish men with prostate cancer and 796 control men reported an association between AR alleles, with more than 22 CAG repeats and prostate cancer (OR, 1.35; 95% CI, 1.08-1.69; P = .03).
An analysis of AR gene CAG and GGN repeat length polymorphisms targeted African American men from the Flint Men's Health Study in an effort to identify a genetic modifier that might help explain the increased risk of prostate cancer in black versus white males in the United States. This population-based study of 131 African American prostate cancer patients and 340 screened-negative African American controls showed no evidence of an association between shorter AR repeat length and prostate cancer risk. These results, together with data from three prior, smaller studies,[134,137,138] indicate that short AR repeat variants do not contribute significantly to the risk of prostate cancer in African American men.
Germline pathogenic variants in the AR gene (located on the X chromosome) have been rarely reported. The R726L pathogenic variant has been identified as a possible contributor to about 2% of both sporadic and familial prostate cancer in Finland. This variant, which alters the transactivational specificity of the AR protein, was found in 8 of 418 (1.91%) consecutive sporadic prostate cancer cases, 2 of 106 (1.89%) familial cases, and 3 of 900 (0.33%) normal blood donors, yielding a significantly increased prostate cancer OR of 5.8 for both case groups. A subsequent Finnish study of 38 early-onset prostate cancer cases and 36 multiple-case prostate cancer families with no evidence of male-to-male transmission revealed one additional R726L pathogenic variant in one of the familial cases and no new germline variants in the AR gene. These investigators concluded that germline AR pathogenic variants explain only a small fraction of familial and early-onset cases in Finland.
A study of genomic DNA from 60 multiple-case African American (n = 30) and white (n = 30) families identified a novel missense germline AR variant, T559S, in three affected members of a black sibship and none in the white families. No functional data were presented to indicate that this variant was clearly deleterious. This was reported as a suggestive finding, in need of additional data.
Steroid 5-alpha-reductase 2gene (SRD5A2)
Molecular epidemiology studies have also examined genetic polymorphisms of the steroid 5-alpha-reductase 2 gene, which is also involved in the androgen metabolism cascade. Two isozymes of 5-alpha-reductase exist. The gene that codes for 5-alpha-reductase type II (SRD5A2) is located on chromosome 2. It is expressed in the prostate, where testosterone is converted irreversibly to dihydrotestosterone (DHT) by 5-alpha-reductase type II. Evidence suggests that 5-alpha-reductase type II activity is reduced in populations at lower risk of prostate cancer, including Chinese and Japanese men.[143,144]
A polymorphism in the untranslated region of the SRD5A2 gene may also be associated with prostate cancer risk. Ten alleles fall into three families that differ in the number of TA dinucleotide repeats.[142,146] Although no clinical significance for these polymorphisms has yet been determined, some TA repeat alleles may promote an elevation of enzyme activity, which may in turn increase the level of DHT in the prostate.[120,142] A subsequent meta-analysis failed to detect a statistically significant association between prostate cancer risk and the TA repeat polymorphism, although a relationship could not be definitively excluded. This meta-analysis also examined the potential roles of two coding variants: A49T and V89L. An association with V89L was excluded, and the role for A49T was found to have at most a modest effect on prostate cancer susceptibility. Bias or chance could account for the latter observation. A study of 1,461 Swedish men with prostate cancer and 796 control men reported an association between two variants in SRD5A2 and prostate cancer risk (OR, 1.45; 95% CI, 1.01-2.08; OR, 1.49; 95% CI, 1.03-2.15). Another meta-analysis of 25 case-control studies, including 8,615 cases and 9,089 controls, found no overall association between the V89L polymorphism and prostate cancer risk. In a subgroup analysis, men younger than 65 years (323 cases and 677 controls) who carried the LL genotype had a modest association with prostate cancer (LL vs. VV, OR, 1.70; 95% CI, 1.09-2.66 and LL vs. VV+VL, OR, 1.75; 95% CI, 1.14-2.68). A subsequent systematic review and meta-analysis including 27 nonfamilial case-control studies found no statistically significant association between either the V89L or A49T polymorphisms and prostate cancer risk.
Polymorphisms in several genes involved in the biosynthesis, activation, metabolism, and degradation of androgens (CYP17, CYP3A4, CYP19A1, and SRD5A2) and the stimulation of mitogenic and antiapoptotic activities (IGF-1 and IGFBP-3) of normal prostate cells were examined for association with prostate cancer in 131 African American cases and 342 controls. While allele frequencies did not differ between cases and controls regarding three SNPs in the CYP17 gene (rs6163, rs6162, and rs743572), heterozygous genotypes of these SNPs were found to be associated with a reduced risk (OR, 0.56; 95% CI, 0.35-0.88; OR, 0.57; 95% CI, 0.36-0.90; OR, 0.55; 95% CI, 0.35-0.88, respectively). Evidence suggestive of an association between SNP rs5742657 in intron 2 of IGF-1 was also found (OR, 1.57; 95% CI, 0.94-2.63). Additional studies are needed to confirm these findings.
Other investigators have explored the potential contribution of the variation in genes involved in the estrogen pathway. A Swedish population study of 1,415 prostate cancer cases and 801 age-matched controls examined the association of SNPs in the estrogen receptor-beta (ER-beta) gene and prostate cancer. One SNP in the promoter region of ER-beta, rs2987983, was associated with an overall prostate cancer risk of 1.23 and 1.35 for localized disease. This study awaits replication.
Germline pathogenic variants in the tumor suppressor gene E-cadherin (also called CDH1) cause a hereditary form of gastric carcinoma. A SNP designated -160?A, located in the promoter region of E-cadherin, has been found to alter the transcriptional activity of this gene. Because somatic pathogenic variants in E-cadherin have been implicated in the development of invasive malignancies in a number of different cancers, investigators have searched for evidence that this functionally significant promoter might be a modifier of cancer risk. A meta-analysis of 47 case-control studies in 16 cancer types included ten prostate cancer cohorts (3,570 cases and 3,304 controls). The OR of developing prostate cancer among risk allele carriers was 1.33 (95% CI, 1.11-1.60). However, the authors of the study noted that there are sources of bias in the dataset, stemming mostly from the small sample sizes of individual cohorts. Additional studies are required to determine whether this finding is reproducible and biologically and clinically important.
Toll-like receptor genes
There is a great deal of interest in the possibility that chronic inflammation may represent an important risk factor in prostate carcinogenesis. The family of toll-like receptors has been recognized as a critical component of the intrinsic immune system, one which recognizes ligands from exogenous microbes and a variety of endogenous substrates. This family of genes has been studied most extensively in the context of autoimmune disease, but there also have been a series of studies that have analyzed genetic variants in various members of this pathway as potential prostate cancer risk modifiers.[157,158,159,160,161] The results have been inconsistent, ranging from decreased risk, to null association, to increased risk.
One study was based upon 1,414 incident prostate cancer cases and 1,414 age-matched controls from the American Cancer Society Cancer Prevention Study II Nutrition Cohort. These investigators genotyped 28 SNPs in a region on chromosome 4p14 that includes TLR-10, TLR-1, and TLR-6, three members of the toll-like receptor gene cluster. Two TLR-10 SNPs and four TLR-1 SNPs were associated with significant reductions in prostate cancer risk, ranging from 29% to 38% for the homozygous variant genotype. A more detailed analysis demonstrated these six SNPs were not independent in their effect, but rather represented a single strong association with reduced risk (OR, 0.55; 95% CI, 0.33-0.90). There were no significant differences in this association when covariates such as Gleason score, history of benign prostatic hypertrophy, use of nonsteroidal anti-inflammatory drugs, and body mass index were taken into account. This is the largest study undertaken to date and included the most comprehensive panel of SNPs evaluated in the 4p14 region. While these observations provide a basis for further investigation of the toll-like receptor genes in prostate cancer etiology, inconsistencies with the prior studies and lack of information regarding what the biological basis of these associations might be warrant caution in interpreting the findings.
Other genes and polymorphisms interrogated for risk
SNPs in genes involved in the steroid hormone pathway have previously been studied in sporadic and familial prostate cancer using a sample of individuals with primarily Caucasian ancestry. Another study evaluated 116 tagging SNPs located in 12 genes in the steroid hormone pathway for risk of prostate cancer in 886 cases and 1,566 controls encompassing non-Hispanic white men, Hispanic white men, and African American men. The genes included CYP17, HSD17B3, ESR1, SRD5A2, HSD3B1, HSD3B2, CYP19, CYP1A1, CYP1B1, CYP3A4, CYP27B1, and CYP24A1. Several SNPs in CYP19 were associated with prostate cancer risk in all three populations. Analysis of SNP-SNP interactions involving SNPs in multiple genes revealed a seven-SNP interaction involving HSD17B3, CYP19, and CYP24A1 in Hispanic whites (P = .001). In non-Hispanic whites, an interaction of four SNPs in HSD3B2, HSD17B3, and CYP19 was found (P < .001). In African Americans, SNPs within SRD5A2, HSD17B3, CYP17, CYP27B1, CYP19, and CYP24A1 showed a significant interaction (P = .014). In non-Hispanic whites, a cumulative risk of prostate cancer was observed for men carrying risk alleles at three SNPs in HSD3B2 and CYP19 (OR, 2.20; 95% CI, 1.44-3.38; P = .0003). In Hispanic whites, a cumulative risk of prostate cancer was observed for men carrying risk alleles at two SNPs in CYP19 and CYP24A1 (OR, 4.29; 95% CI, 2.11-8.72; P = .00006). While this study did not evaluate all potentially important SNPs in genes in the steroid hormone pathway, it demonstrates how studies can be performed to evaluate multigenic effects in multiple populations to assess the contribution to prostate cancer risk.
A meta-analysis of the relationship between eight polymorphisms in six genes (MTHFR, MTR, MTHFD1, SLC19A1, SHMT1, and FOLH1) from the folate pathway was conducted by pooling data from eight case-control studies, four GWAS, and a nested case-control study named Prostate Testing for Cancer and Treatment in the United Kingdom. Numbers of tested subjects varied among these polymorphisms, with up to 10,743 cases and 35,821 controls analyzed. The report concluded that known common folate-pathway SNPs do not have significant effects on prostate cancer susceptibility in white men.
Four SNPs in the p53 pathway (three in genes regulating p53 function including MDM2, MDM4, and HAUSP and one in p53) were evaluated for association with aggressive prostate cancer in a hospital-based prostate cancer cohort of men with Caucasian ethnicity (N = 4,073). However, a subsequent meta-analysis of case-control studies that focused on MDM2 (T309G) and prostate cancer risk revealed no association. Therefore, the biologic basis of the various associations identified requires further study.
Table 3 summarizes additional case-control studies that have assessed genes that are potentially associated with prostate cancer susceptibility.
Case-control studies assessed site-specific prostate cancer susceptibility in the following genes: EMSY, KLF6, AMACR, NBN, CHEK2, AR, SRD5A2, ER-beta, E-cadherin, and the toll-like receptor genes. These studies have been complicated by the later-onset nature of the disease and the high background rate of prostate cancer in the general population. In addition, there is likely to be real, extensive locus heterogeneity for hereditary prostate cancer, as suggested by both segregation and linkage studies. In this respect, hereditary prostate cancer resembles a number of the other major adult-onset hereditary cancer syndromes, in which more than one gene can produce the same or very similar clinical phenotype (e.g., hereditary breast/ovarian cancer, Lynch syndrome, hereditary melanoma, and hereditary renal cancer). The clinical validity and utility of genetic testing for any of these genes based solely on evidence for hereditary prostate cancer susceptibility has not been established.
Admixture mapping is a method used to identify genetic variants associated with traits and/or diseases in individuals with mixed ancestry. This approach is most effective when applied to individuals whose admixture was recent and consists of two populations who had previously been separated for thousands of years. The genomes of such individuals are a mosaic, comprised of large blocks from each ancestral locale. The technique takes advantage of a difference in disease incidence in one ancestral group compared with another. Genetic risk loci are presumed to reside in regions enriched for the ancestral group with higher incidence. Successful mapping depends on the availability of population-specific genetic markers associated with ancestry, and on the number of generations since admixture.[179,180]
Admixture mapping is a particularly attractive method for identifying genetic loci associated with increased prostate cancer risk among African Americans. African American men are at higher risk of developing prostate cancer than are men of European ancestry, and the genomes of African American men are mosaics of regions from Africa and regions from Europe. It is therefore hypothesized that inherited variants accounting for the difference in incidence between the two groups must reside in regions enriched for African ancestry. In prostate cancer admixture studies, genetic markers for ancestry were genotyped genome-wide in African American cases and controls in a search for areas enriched for African ancestry in the men with prostate cancer. Admixture studies have identified the following chromosomal regions associated with prostate cancer:
An advantage of this approach is that recent admixtures result in long stretches of linkage disequilibrium (up to hundreds of thousands of base pairs) of one particular ancestry. As a result, fewer markers are needed to search for genetic variants associated with specific diseases, such as prostate cancer, than the number of markers needed for successful GWAS. (Refer to the GWAS section of this summary for more information.)
Genome-wide Association Studies (GWAS)
Introduction to GWAS
Genome-wide searches have successfully identified susceptibility alleles for many complex diseases, including prostate cancer. This approach can be contrasted with linkage analysis, which searches for genetic risk variants co-segregating within families that have a high prevalence of disease. Linkage analyses are designed to uncover rare, highly penetrant variants that segregate in predictable heritance patterns (e.g., autosomal dominant, autosomal recessive, X-linked, and mitochondrial). GWAS, on the other hand, are best suited to identify multiple, common, low-penetrance genetic polymorphisms. GWAS are conducted under the assumption that the genetic underpinnings of complex phenotypes, such as prostate cancer, are governed by many alleles, each conferring modest risk. Most genetic polymorphisms genotyped in GWAS are common, with minor allele frequencies greater than 1% to 5% within a given ancestral population (e.g., men of European ancestry). GWAS survey all common inherited variants across the genome, searching for alleles that are associated with incidence of a given disease or phenotype.[184,185] The strong correlation between many alleles located close to one another on a given chromosome (called linkage disequilibrium) allows one to "scan" the genome without having to test all tens of millions of known SNPs. GWAS can test approximately 1 million to 5 million SNPs and ascertain almost all common inherited variants in the genome.
In a GWAS, allele frequency is compared for each SNP between cases and controls. Promising signals-in which allele frequencies deviate significantly in case compared to control populations-are validated in replication cohorts. In order to have adequate statistical power to identify variants associated with a phenotype, large numbers of cases and controls, typically thousands of each, are studied. Because 1 million SNPs are typically evaluated in a GWAS, false-positive findings are expected to occur frequently when standard statistical thresholds are used. Therefore, stringent statistical rules are used to declare a positive finding, usually using a threshold of P < 1 × 10-7.[186,187,188]
To date, over 100 variants associated with prostate cancer have been identified by well-powered GWAS and validated in independent cohorts (refer to the National Human Genome Research Institute GWAS catalog and ). These studies have revealed convincing associations between specific inherited variants and prostate cancer risk. In addition, men with early-onset prostate cancer have a higher cumulative number of risk alleles compared with older prostate cancer cases and compared with public controls. However, the findings should be qualified with a few important considerations:
The implications of these points are discussed in greater detail below. Additional detail can be found elsewhere.
Susceptibility loci identified in GWAS
Beginning in 2006, multiple genome-wide studies seeking associations with prostate cancer risk converged on the same chromosomal locus, 8q24. The population-attributable risk of prostate cancer from these alleles was 8%. The results were replicated in European American, African American, Icelandic, and Swedish populations.[68,70,71,72,73,74,75,80,81,82,83,195,86,87] In all, approximately nine genetic polymorphisms, all independently associated with disease, reside within five distinct 8q24 risk regions.[86,87]
Since the discovery of prostate cancer risk loci at 8q24, more than 100 variants at other chromosomal risk loci similarly have been identified by multistage GWAS comprised of thousands of cases and controls and validated in independent cohorts. The most convincing associations reported to date for men of European ancestry are annotated in the National Human Genome Research Institute GWAS catalog.
GWAS in populations of non-European ancestry
Most prostate cancer GWAS data generated to date have been derived from populations of European descent. This shortcoming is profound, considering that linkage disequilibrium structure, SNP frequencies, and incidence of disease differ across ancestral groups. To provide meaningful genetic data to all patients, well-designed, adequately powered GWAS must be aimed at specific ethnic groups. Most work in this regard has focused on African American, Chinese, and Japanese men. The most convincing associations reported to date for men of non-European ancestry are annotated in the National Human Genome Research Institute GWAS catalog.
The African American population is of particular interest because American men with African ancestry are at higher risk of prostate cancer than any other group. In addition, inherited variation at the 8q24 risk locus appears to contribute to differences in African American and European American incidence of disease. A handful of studies have sought to determine whether GWAS findings in men of European ancestry are applicable to men of African ancestry. One study interrogated 28 known prostate cancer risk loci via fine mapping in 3,425 African American cases and 3,290 African American controls. Another study examined 82 previously reported risk variants in 4,853 prostate cancer cases and 4,678 controls. The majority of risk alleles (approximately 83%) are shared across African American and European American populations.
Statistically well-powered GWAS have also been launched to examine inherited cancer risk in Japanese and Chinese populations. Investigators discovered that these populations share many risk regions observed in African American men in other studies.[199,200,201] Additionally, risk regions that are unique to these ancestral groups were identified. Ongoing work in larger cohorts will validate and expand upon these findings.
Clinical application of GWAS findings
Because the variants discovered by GWAS are markers of risk, there has been great interest in using genotype as a screening tool to predict the development of prostate cancer. As increasing numbers of risk SNPs have been discovered, they have been applied to clinical cohorts alongside traditional variables such as PSA and family history. An initial study of the first five known risk SNPs could not demonstrate that they added clinically meaningful data. In later trials, larger risk-SNP panels also could not demonstrate usefulness for a large proportion of the screening population. However, the small subset of men carrying large numbers of risk alleles, especially those with positive family histories, were at appreciably high risk of developing prostate cancer.[78,202]
In July 2012, the Agency for Healthcare Research and Quality (AHRQ) published a report that sought to address the clinical utility of germline genotyping of prostate cancer risk markers discovered by GWAS. Largely on the basis of the evidence from the studies described above, AHRQ concluded that established prostate cancer risk SNPs have "poor discriminative ability" to identify individuals at risk of developing the disease. Similarly, the authors of another study estimated that the contribution of GWAS polymorphisms in determining the risk of developing prostate cancer will be modest, even as meta-analyses or larger studies uncover additional "common" risk alleles (alleles carried by >1%-5% of individuals within the population).
By 2014, approximately 100 bona fide prostate cancer risk variants had been annotated. A polygenic risk score comprising the full complement of known risk SNPs has been proposed that could account for a 2.9-fold increase in prostate cancer risk among men in the top 10% risk stratum and a 5.7-fold risk increase among men in top 1% risk stratum, compared with the population average. The authors concluded that targeted germline genetic testing, perhaps focusing on men with a family history of prostate cancer, may help improve the accuracy of PSA screening. Larger cohorts have validated the finding that those at the extremes of risk allele status carry appreciably greater or less prostate cancer risk, though these subsets represent a very small fraction of the overall screening population.[205,206] A 2016 analysis of a collection of risk variants suggested an association between cumulative risk allele status and early-onset prostate cancer.
GWAS findings to date account for only 33% to 50% of heritable risk of disease. Research is ongoing to uncover the remaining portion of genetic risk. This includes the discovery of rarer alleles with higher ORs for risk.
In addition, other genetic polymorphisms, such as copy number variants, are becoming increasingly amenable to testing. As the full picture of inherited prostate cancer risk becomes more complete, it is hoped that germline information will become clinically useful. Finally, GWAS are providing more insight into the mechanism of prostate cancer risk. Notably, almost all reported prostate cancer risk alleles reside in nonprotein-coding regions of the genome; however, the underlying biological mechanism of disease susceptibility was initially unclear. It is now apparent that a large proportion of risk variants affect the activity of regulatory elements and, in turn, distal genes.[209,210,211,212,212,213,214,215,216,217] As GWAS elucidate these networks, it is hoped that new therapies and chemopreventive strategies will follow.
Modified approaches to GWAS
A 2012 study used a novel approach to identify polymorphisms associated with risk. On the basis of the well-established principle that the AR plays a prominent role in prostate tumorigenesis, the investigators targeted SNPs that reside at sites where the AR binds to DNA. They leveraged data from previous studies that mapped thousands of AR binding sites genome-wide in prostate cancer cell lines to select SNPs to genotype in the Johns Hopkins Hospital cohort of 1,964 cases and 3,172 controls and the Cancer Genetic Markers of Susceptibility cohort of 1,172 cases and 1,157 controls. This modified GWAS revealed a SNP (rs4919743) located at the KRT8 locus at 12q13.13-a locus previously implicated in cancer development-associated with prostate cancer risk, with an OR of 1.22 (95% CI, 1.13-1.32). The study is notable for its use of a reasonable hypothesis and prior data to guide a genome-wide search for risk variants. Other approaches include evaluating SNPs implicated in a phenotype other than prostate cancer.[219,220]
Although the statistical evidence for an association between genetic variation at these loci and prostate cancer risk is overwhelming, the clinical relevance of the variants and the mechanism(s) by which they lead to increased risk are unclear and will require further characterization. Additionally, these loci are associated with very modest risk estimates and explain only a fraction of overall inherited risk. Further work will include genome-wide analysis of rarer alleles catalogued via sequencing efforts, such as the 1000 Genomes Project. Disease-associated alleles with frequencies of less than 1% in the population may prove to be more highly penetrant and clinically useful. In addition, further work is needed to describe the landscape of genetic risk in non-European populations. Finally, until the individual and collective influences of genetic risk alleles are evaluated prospectively, their clinical utility will remain difficult to fully assess.
Inherited Variants Associated With Prostate Cancer Aggressiveness
Prostate cancer is biologically and clinically heterogeneous. Many tumors are indolent and are successfully managed with observation alone. Other tumors are quite aggressive and prove deadly. Several variables are used to determine prostate cancer aggressiveness at the time of diagnosis, such as Gleason score and PSA, but these are imperfect. Additional markers are needed because sound treatment decisions depend on accurate prognostic information. Germline genetic variants are attractive markers because they are present, easily detectable, and static throughout life.
Findings to date regarding inherited risk of aggressive disease are considered preliminary. As described below, germline SNPs associated with prostate cancer aggressiveness are derived primarily from three methods of analysis: 1) annotation of common variants within candidate risk genes; 2) assessment of known overall prostate cancer risk SNPs for aggressiveness; and 3) GWAS for prostate cancer aggressiveness. Further work is needed to validate findings and assess these associations prospectively.
Like studies of the genetics of overall prostate cancer risk, initial studies of inherited risk of aggressive prostate cancer focused on polymorphisms in candidate genes.[166,222,223,224,225,226,227] Next, as GWAS revealed prostate cancer risk SNPs, several research teams sought to determine whether certain overall risk SNPs were also associated with aggressiveness.[228,229,230,231,232,233,234,235]
There has been great interest in launching more unbiased, genome-wide searches for inherited variants associated with indolent versus aggressive prostate cancer.
Associations between inherited variants and prostate cancer aggressiveness have been reported. A multistage, case-only GWAS led by the National Cancer Institute examined 12,518 prostate cancer cases and discovered an association between genotype and Gleason score at two polymorphisms: rs35148638 at 5q14.3 (RASA1, P = 6.49 × 10-9) and rs78943174 at 3q26.31 (NAALADL2, P = 4.18 × 10-8). Although the associations discovered in this trial may provide valuable insight into the biology of high-grade disease, it is unclear whether they will prove clinically useful. This study raises the issue of the definition of "prostate cancer aggressiveness." Gleason score is used as a prognostic marker but is not a perfect surrogate for prostate cancer-specific survival or overall survival.
A few GWAS designed specifically to focus on prostate cancer subjects with documented disease-related outcomes have been launched. In one study-a genome-wide analysis in which two of the largest international prostate cancer genotyped cohorts were combined for analysis (24,023 prostate cancer cases, including 3,513 disease-specific deaths)-no SNP was significantly associated with prostate cancer-specific survival. Similarly, in a smaller study assessing prostate cancer-specific mortality (196 lethal cases, 368 long-term survivors), no variants were significantly associated with outcome. More recently, a GWAS was conducted across 24,023 prostate cancer patients and similarly found no significant association between genetic variants and prostate cancer survival. The authors of these studies concluded that any SNP associated with prostate cancer outcome must be fairly rare in the general population (minor allele frequency below 1%).
Genetic testing for pathogenic variants in genes with some association with prostate cancer risk is now available and has the potential to identify those at increased risk of prostate cancer. Research from selected cohorts has reported that prostate cancer risk is elevated in men with pathogenic variants in BRCA1, BRCA2, and on a smaller scale, in mismatch repair (MMR) genes. Since clinical genetic testing is available for these genes, information about risk of prostate cancer based on alterations in these genes is included in this section. In addition, pathogenic variants in HOXB13 are reported to account for a small proportion of hereditary prostate cancer. Clinical testing for HOXB13 alterations is also available; therefore, this gene is included in this section.
It is possible that additional genes will have clinical relevance in prostate cancer risk in the future. Clinical sequencing of 150 metastatic tumors from men with castrate-resistant prostate cancer identified alterations in genes involved in DNA repair in 23% of men. Interestingly, 8% of these variants were present in the germline. Although this work has not been confirmed, it raises the possibility that identification of certain germline variants may have clinical relevance in the near future.
Studies of male carriers of BRCA1 and BRCA2 pathogenic variants demonstrate that these individuals have a higher risk of prostate cancer and other cancers. Prostate cancer in particular has been observed at higher rates in male carriers of BRCA2 pathogenic variants than in the general population.
BRCA-associated prostate cancer risk
The risk of prostate cancer in carriers of BRCA pathogenic variants has been studied in various settings.
In an effort to clarify the relationship between BRCA pathogenic variants and prostate cancer risk, findings from several case series are summarized in Table 4.
Estimates derived from the Breast Cancer Linkage Consortium may be overestimated because these data are generated from a highly select population of families ascertained for significant evidence of risk of breast cancer and ovarian cancer and suitability for linkage analysis. However, a review of the relationship between germline pathogenic variants in BRCA2 and prostate cancer risk supports the view that this gene confers a significant increase in risk among male members of hereditary breast and ovarian cancer families but that it likely plays only a small role, if any, in site-specific, multiple-case prostate cancer families. In addition, the clinical validity and utility of BRCA testing solely on the basis of evidence for hereditary prostate cancer susceptibility has not been established.
One study has assessed the relationship between germline DNA repair gene pathogenic variants and metastatic prostate cancer. Of 692 men unselected for cancer family history or age at diagnosis, 5.3% (37 of 692) were found to have a BRCA2 pathogenic variant, and 0.9% (6 of 692) had a BRCA1 pathogenic variant.
Prevalence ofBRCAfounder pathogenic variants in men with prostate cancer
Ashkenazi Jewish population
Several studies in Israel and in North America have analyzed the frequency of BRCAfounder pathogenic variants among Ashkenazi Jewish (AJ) men with prostate cancer.[9,10,11] Two specific BRCA1 pathogenic variants (185delAG and 5382insC) and one BRCA2 pathogenic variant (6174delT) are common in individuals of AJ ancestry. Carrier frequencies for these pathogenic variants in the general Jewish population are 0.9% (95% CI, 0.7-1.1) for the 185delAG pathogenic variant, 0.3% (95% confidence interval [CI], 0.2-0.4) for the 5382insC pathogenic variant, and 1.3% (95% CI, 1.0-1.5) for the BRCA2 6174delT pathogenic variant.[12,13,14,15] (Refer to the High-Penetrance Breast and/or Gynecologic Cancer Susceptibility Genes section in the PDQ summary on Genetics of Breast and Gynecologic Cancers for more information about BRCA1 and BRCA2 genes.) In these studies, the relative risks (RRs) were commonly greater than 1, but only a few have been statistically significant. Many of these studies were not sufficiently powered to rule out a lower, but clinically significant, risk of prostate cancer in carriers of Ashkenazi BRCA founder pathogenic variants.
In the Washington Ashkenazi Study (WAS), a kin-cohort analytic approach was used to estimate the cumulative risk of prostate cancer among more than 5,000 American AJ male volunteers from the Washington, District of Columbia, area who carried one of the BRCA Ashkenazi founder pathogenic variants. The cumulative risk to age 70 years was estimated to be 16% (95% CI, 4-30) among carriers of the founder pathogenic variants and 3.8% among noncarriers (95% CI, 3.3-4.4). This fourfold increase in prostate cancer risk was equal (in absolute terms) to the cumulative risk of ovarian cancer among female carriers at the same age (16% by age 70 years; 95% CI, 6-28). The risk of prostate cancer in male carriers in the WAS cohort was elevated by age 50 years, was statistically significantly elevated by age 67 years, and increased thereafter with age, suggesting both an overall excess in prostate cancer risk and an earlier age at diagnosis among carriers of Ashkenazi founder pathogenic variants. Prostate cancer risk differed depending on the gene, with BRCA1 pathogenic variants associated with increasing risk after age 55 to 60 years, reaching 25% by age 70 years and 41% by age 80 years. In contrast, prostate cancer risk associated with the BRCA2 pathogenic variant began to rise at later ages, reaching 5% by age 70 years and 36% by age 80 years (numeric values were provided by the author [written communication, April 2005]).
The studies summarized in Table 5 used similar case-control methods to examine the prevalence of Ashkenazi founder pathogenic variants among Jewish men with prostate cancer and found an overall positive association between carrier status of founder pathogenic variants and prostate cancer risk.
These studies support the hypothesis that prostate cancer occurs excessively among carriers of AJ founder pathogenic variants and suggest that the risk may be greater among men with the BRCA2 founder pathogenic variant (6174delT) than among those with one of the BRCA1 founder pathogenic variants (185delAG; 5382insC). The magnitude of the BRCA2-associated risks differ somewhat, undoubtedly because of interstudy differences related to participant ascertainment, calendar time differences in diagnosis, and analytic methods. Some data suggest that BRCA-related prostate cancer has a significantly worse prognosis than prostate cancer that occurs among noncarriers.
The association between prostate cancer and pathogenic variants in BRCA1 and BRCA2 has also been studied in other populations. Table 6 summarizes studies that used case-control methods to examine the prevalence of BRCA pathogenic variants among men with prostate cancer from other varied populations.
These data suggest that prostate cancer risk in carriers of BRCA1/BRCA2 pathogenic variants varies with the location of the pathogenic variant (i.e., there is a correlation between genotype and phenotype).[20,21,23] These observations might explain some of the inconsistencies encountered in prior studies of these associations, since varied populations may have differences in the proportion of persons with specific BRCA1/BRCA2 pathogenic variants.
Several case series have also explored the role of BRCA1 and BRCA2 pathogenic variants and prostate cancer risk.
These case series confirm that pathogenic variants in BRCA1 and BRCA2 do not play a significant role in hereditary prostate cancer. However, germline pathogenic variants in BRCA2 account for some cases of early-onset prostate cancer, although this is estimated to be less than 1% of early-onset prostate cancers in the United States.
Prostate cancer aggressiveness in carriers ofBRCApathogenic variants
The studies summarized in Table 8 used similar case-control methods to examine features of prostate cancer aggressiveness among men with prostate cancer found to harbor a BRCA1/BRCA2 pathogenic variant.
These studies suggest that prostate cancer in carriers of BRCA pathogenic variants may be associated with features of aggressive disease, including higher Gleason score, higher prostate-specific antigen (PSA) level at diagnosis, and higher tumor stage and/or grade at diagnosis , a finding that warrants consideration as patients undergo cancer risk assessment and genetic counseling. Research is under way to gain insight into the biologic basis of aggressive prostate cancer in carriers of BRCA pathogenic variants. One study of 14 BRCA2 germline pathogenic variant carriers reported that BRCA2-associated prostate cancers harbor increased genomic instability and a mutational pro?le that more closely resembles metastatic prostate cancer than localized disease, with genomic and epigenomic dysregulation of the MED12L/MED12 axis similar to metastatic castration-resistant prostate cancer.
BRCA1/BRCA2and survival outcomes
Analyses of prostate cancer cases in families with known BRCA1 or BRCA2 pathogenic variants have been examined for survival. In an unadjusted analysis performed on a case series, median survival was 4 years in 183 men with prostate cancer with a BRCA2 pathogenic variant and 8 years in 119 men with a BRCA1 pathogenic variant. The study suggests that carriers of BRCA2 pathogenic variants have a poorer survival than carriers of BRCA1 pathogenic variants. To further assess this observation, case-control studies were conducted (summarized in Table 9).
These findings suggest overall survival and prostate cancer-specific survival may be lower in carriers of pathogenic variants than in controls.
Additional studies involving theBRCAregion
A genome-wide scan for hereditary prostate cancer using 175 families from the University of Michigan Prostate Cancer Genetics Project (UM-PCGP) found evidence of linkage to chromosome 17q markers. The maximum logarithm of the odds (LOD) score in all families was 2.36, and the LOD score increased to 3.27 when only families with four or more confirmed affected men were analyzed. The linkage peak was centered over the BRCA1 gene. In follow-up, these investigators screened the entire BRCA1 gene for pathogenic variants using DNA from one individual from each of 93 pedigrees with evidence of prostate cancer linkage to 17q markers. Sixty-five of the individuals screened had wild-type BRCA1 sequence, and only one individual from a family with prostate and ovarian cancers was found to have a truncating pathogenic variant (3829delT). The remainder of the individuals harbored one or more germline BRCA1 variants, including 15 missense variants of uncertain clinical significance. The conclusion from these two reports is that there is evidence of a prostate cancer susceptibility gene on chromosome 17q near BRCA1; however, large deleterious inactivating variants in BRCA1 are not likely to be associated with prostate cancer risk in chromosome 17-linked families.
In another study from the UM-PCGP, common genetic variation in BRCA1 was examined. Conditional logistic regression analysis and family-based association tests were performed in 323 familial prostate cancer families and early-onset prostate cancer families, which included 817 men with and without prostate cancer, to investigate the association of single nucleotide polymorphisms (SNPs) tagging common haplotype variation in a 200-kilobase region surrounding and including BRCA1. Three SNPs in BRCA1 (rs1799950, rs3737559, and rs799923) were found to be associated with prostate cancer. The strongest association was observed for SNP rs1799950 (odds ratio [OR], 2.25; 95% CI, 1.21-4.20), which leads to a glutamine-to-arginine substitution at codon 356 (Gln356Arg) of exon 11 of BRCA1. Furthermore, SNP rs1799950 was found to contribute to the linkage signal on chromosome 17q21 originally reported by the UM-PCGP.
Mismatch Repair (MMR) Genes
Five genes are implicated in MMR, namely MLH1, MSH2, MSH6, PMS2, and EPCAM. Germline pathogenic variants in these five genes have been associated with Lynch syndrome, which manifests by cases of nonpolyposis colorectal cancer and a constellation of other cancers in families, including endometrial, ovarian, and duodenal cancers; and transitional cell cancers of the ureter and renal pelvis. Reports have suggested that prostate cancer may be observed in men harboring an MMR gene pathogenic variant.[40,41] The first quantitative study described nine cases of prostate cancer occurring in a population-based cohort of 106 Norwegian male carrier of MMR gene pathogenic variants or obligate carriers. The expected number of cases among these 106 men was 1.52 (P < .01); the men were younger at the time of diagnosis (60.4 years vs. 66.6 years, P = .006) and had more evidence of Gleason score of 8 to 10 (P < .00001) than the cases from the Norwegian Cancer Registry. Kaplan Meier analysis revealed that the cumulative risk of prostate cancer diagnosis by age 70 years was 30% in carriers of MMR gene pathogenic variants and 8% in the general population. This finding awaits confirmation in additional populations. A population-based case-control study examined haplotype-tagging SNPs in three MMR genes (MLH1, MSH2, and PMS2). This study provided some evidence supporting the contribution of genetic variation in MLH1 and overall risk of prostate cancer. To assess the contribution of prostate cancer as a feature of Lynch syndrome, one study performed microsatellite instability (MSI) testing on prostate cancer tissue blocks from families enrolled in a prostate cancer family registry who also reported a history of colon cancer. Among 35 tissue blocks from 31 distinct families, two tumors from families with MMR gene pathogenic variants were found to be MSI-high. The authors conclude that MSI is rare in hereditary prostate cancer. Other studies are attempting to characterize rates of prostate cancer in Lynch syndrome families and correlate molecular features with prostate cancer risk.
One study that included two familial cancer registries found an increased cumulative incidence and risk of prostate cancer among 198 independent families with MMR gene pathogenic variants and Lynch syndrome. The cumulative lifetime risk of prostate cancer (to age 80 years) was 30.0% in carriers of MMR gene pathogenic variants (95% CI, 16.54-41.30; P = .07), whereas it was 17.84% in the general population, according to the Surveillance, Epidemiology, and End Results Program estimates. There was a trend of increased prostate cancer risk in carriers of pathogenic variants by age 50 years, where the risk was 0.64% (95% CI, 0.24-1.01; P = .06), compared with a risk of 0.26% in the general population. Overall, the hazard ratio (HR) (to age 80 years) for prostate cancer in carriers of MMR gene pathogenic variants in the combined data set was 1.99 (95% CI, 1.31-3.03; P = .0013). Among men aged 20 to 59 years, the HR was 2.48 (95% CI, 1.34-4.59; P = .0038).
A systematic review and meta-analysis that included 23 studies (6 studies with molecular characterization and 18 risk studies, of which 12 studies quantified risk for prostate cancer) reported an association of prostate cancer with Lynch syndrome. In the six molecular studies included in the analysis, 73% (95% CI, 57%-85%) of prostate cancers in carriers of MMR gene pathogenic variants were MMR deficient. The RR of prostate cancer in carriers of MMR gene pathogenic variants was estimated to be 3.67 (95% CI, 2.32-6.67). Of the twelve risk studies, the RR of prostate cancer ranged from 2.11 to 2.28, compared with that seen in the general population depending on carrier status, prior diagnosis of colorectal cancer, or unknown male carrier status from families with a known pathogenic variant.
A study from three sites participating in the Colon Cancer Family Registry examined 32 cases of prostate cancer (mean age at diagnosis, 62 years; standard deviation, 8 years) in men with a documented MMR gene pathogenic variant (23 MSH2 carriers, 5 MLH1 carriers, and 4 MSH6 carriers). Seventy-two percent (n = 23) had a previous diagnosis of colorectal cancer. Immunohistochemistry was used to assess MMR protein loss, which was observed in 22 tumors (69%); the pattern of loss of protein expression was 100% concordant with the germline pathogenic variant. The RR of prostate cancer was highest in carriers of MSH2 pathogenic variants (RR, 5.8 [95% CI, 2.6-20.9]); the RRs in carriers of MLH1 and MSH6 pathogenic variants were 1.7 (95% CI, 1.1-6.7) and 1.3 (95% CI, 1.1-5.3), respectively. Gleason scores ranged from 5 to 10; two tumors had a Gleason score of 5; 22 tumors had a Gleason score of 6 or 7; and eight tumors had a Gleason score higher than 8. Sixty-seven percent (12 of 18) of the tumors were found to have perineural invasion, and 47% (9 of 19) had extracapsular invasion.
Although the risk of prostate cancer appears to be elevated in families with Lynch syndrome, strategies for germline testing for MMR gene pathogenic variants in index prostate cancer patients remain to be determined.
Linkage to 17q21-22 was initially reported by the UM-PCGP from 175 pedigrees of families with hereditary prostate cancer. Fine-mapping of this region provided strong evidence of linkage (LOD score = 5.49) and a narrow candidate interval (15.5 Mb) for a putative susceptibility gene among 147 families with four or more affected men and average age at diagnosis of 65 years or younger. The exons of 200 genes in the 17q21-22 region were sequenced in DNA from 94 unrelated patients from hereditary prostate cancer families (from the UM-PCGP and Johns Hopkins).Probands from four families were discovered to have a recurrent pathogenic variant (G84E) in HOXB13, and 18 men with prostate cancer from these four families carried the pathogenic variant. The pathogenic variant status was determined in 5,083 additional case subjects and 2,662 control subjects. Carrier frequencies and ORs for prostate cancer risk were as follows:
A validation study from the International Consortium of Prostate Cancer Genetics confirmed HOXB13 as a susceptibility gene for prostate cancer risk. Within carrier families, the G84E pathogenic variant was more common among men with prostate cancer than among unaffected men (OR, 4.42; 95% CI, 2.56-7.64). The G84E pathogenic variant was also significantly overtransmitted from parents to affected offspring (P = 6.5 × 10-6).
Additional studies have emerged that better define the carrier frequency, prostate cancer risk, and penetrance associated with the HOXB13 G84E pathogenic variant.[50,52,53,54,55,56,57] To date, this pathogenic variant appears to be restricted to white men, primarily of European descent.[50,52,53,54] The highest carrier frequency of 6.25% was reported in Finnish early-onset cases. A pooled analysis that included 9,016 cases and 9,678 controls of European Americans found an overall G84E pathogenic variant frequency of 1.34% among cases and 0.28% among controls.
Risk of prostate cancer by HOXB13 G84E pathogenic variant status has been reported to vary by age of onset, family history, and geographical region. A validation study in an independent cohort of 9,988 cases and 61,994 controls from six studies of men of European ancestry, including 4,537 cases and 54,444 controls from Iceland whose genotypes were largely imputed, reported an OR of 7.06 (95% CI, 4.62-10.78; P = 1.5 × 10-19) for prostate cancer risk by G84E carrier status. A pooled analysis reported a prostate cancer OR of 4.86 (95% CI, 3.18-7.69; P = 3.48 × 10-17) in men with HOXB13 pathogenic variants compared with noncarriers; this increased to an OR of 8.41 (95% CI, 5.27-13.76; P = 2.72 ×10-22) among men diagnosed with prostate cancer at age 55 years or younger. The OR was 7.19 (95% CI, 4.55-11.67; P = 9.3 × 10-21) among men with a positive family history of prostate cancer and 3.09 (95% CI, 1.83-5.23; P = 6.26 × 10-6) among men with a negative family history of prostate cancer. A meta-analysis that included 24,213 cases and 73,631 controls of European descent revealed an overall OR for prostate cancer by carrier status of 4.07 (95% CI, 3.05-5.45; P < .00001). Risk of prostate cancer varied by geographical region: United States (OR, 5.10; 95% CI, 3.21-8.10; P < .00001), Canada (OR, 5.80; 95% CI, 1.27-26.51; P = .02), Northern Europe (OR, 3.61; 95% CI, 2.81-4.64; P < .00001), and Western Europe (OR, 8.47; 95% CI, 3.68-19.48; P < .00001). In addition, the association between the G84E pathogenic variant and prostate cancer risk was higher for early-onset cases (OR, 10.11; 95% CI, 5.97-17.12). There was no significant association with aggressive disease in the meta-analysis.
Another meta-analysis that included 11 case-control studies also reported higher risk estimates for prostate cancer in HOXB13 G84E carriers (OR, 4.51; 95% CI, 3.28-6.20; P < .00001) and found a stronger association between HOXB13 G84E and early-onset disease (OR, 9.73; 95% CI, 6.57-14.39; P < .00001). An additional meta-analysis of 25 studies including 51,390 cases and 93,867 controls revealed an OR for prostate cancer of 3.248 (95% CI, 2.121-3.888). The association was most significant in Caucasians (OR, 2.673; 95% CI, 1.920-3.720), especially those of European descent. No association was found for breast or colorectal cancer. One population-based, case-control study from the United States confirmed the association of the G84E pathogenic variant with prostate cancer (OR, 3.30; 95% CI, 1.21-8.96) and reported a suggestive association with aggressive disease. In addition, one study identified no men of Ashkenazi Jewish ancestry who carried the G84E pathogenic variant. A case-control study from the U.K. that included 8,652 cases and 5,252 controls also confirmed the association of HOXB13 G84E with prostate cancer (OR, 2.93; 95% CI, 1.94-4.59; P = 6.27 × 10-8). The risk was higher among men with a family history (OR, 4.53; 95% CI, 2.86-7.34; P = 3.1 × 10-8] and in early-onset prostate cancer (diagnosed at age 55 years or younger) (OR, 3.11; 95% CI, 1.98-5.00; P = 6.1 × 10-7). No association was found between carrier status and Gleason score, cancer stage, overall survival, or cancer-specific survival.
Penetrance estimates for prostate cancer development in carriers of the HOXB13 G84E pathogenic variant are also being reported. One study from Sweden estimated a 33% lifetime risk of prostate cancer among G84E carriers. Another study from Australia reported age-specific cumulative risk of prostate cancer of up to 60% by age 80 years.
HOXB13 plays a role in prostate cancer development and interacts with the androgen receptor; however, the mechanism by which it contributes to the pathogenesis of prostate cancer remains unknown. This is the first gene identified to account for a fraction of hereditary prostate cancer, particularly early-onset prostate cancer. The clinical utility and implications for genetic counseling regarding the HOXB13 G84E pathogenic variant have yet to be defined.
Multigene (Panel) Testing in Prostate Cancer
Since the availability of next-generation sequencing and the elimination of patent restrictions, several clinical laboratories now offer genetic testing through multigene panels at a cost comparable to single-gene testing. A caveat is the possible finding of a variant of uncertain significance, where the clinical significance remains unknown. (Refer to the Multigene [panel] testing section in the PDQ summary on Cancer Genetics Risk Assessment and Counseling for more information about multigene testing, including genetic education and counseling considerations and research examining the use of multigene testing.) This section summarizes the evidence for additional genes that may be on prostate cancer susceptibility panel tests.
One retrospective case series of 692 men with metastatic prostate cancer unselected for cancer family history or age at diagnosis assessed the incidence of germline pathogenic variants in 16 DNA repair genes. Pathogenic variants were identified in 11.8% (82 of 692), a rate higher than in men with localized prostate cancer (4.6%, P < .001), suggesting that genetic aberrations are more commonly observed in men with aggressive forms of disease.
Ataxia telangiectasia (AT) (OMIM) is an autosomal recessive disorder characterized by neurologic deterioration, telangiectasias, immunodeficiency states, and hypersensitivity to ionizing radiation. It is estimated that 1% of the general population may be heterozygote carriers of ATM variants (OMIM). In the presence of DNA damage, the ATM protein is involved in mediating cell cycle arrest, DNA repair, and apoptosis. Given evidence of other cancer risks in heterozygote carriers, evidence of an association with prostate cancer susceptibility continues to emerge. (Refer to the ATM section in the PDQ summary on Genetics of Breast and Gynecologic Cancers for more information about ATM and breast cancer.) A prospective case series of 10,317 Danish individuals with 36 years of follow-up, during which 2,056 individuals developed cancer, found that Ser49Cys was associated with prostate cancer (HR, 2.3; 95% CI, 1.1-5.0). A retrospective case series of 692 men with metastatic prostate cancer unselected for cancer family history or age at diagnosis found that 1.6% (11 of 692) had an ATM pathogenic variant.
CHEK2 has also been investigated for a potential association with prostate cancer risk. (Refer to Table 3 for information about case-control studies that have assessed CHEK2 as a potential prostate cancer susceptibility gene.) A retrospective case series of 692 men with metastatic prostate cancer unselected for cancer family history or age at diagnosis found 1.9% (10 of 534 [men with data]) were found to have a CHEK2 pathogenic variant.
TP53 has also been investigated for a potential association with prostate cancer risk. In a case series of 286 individuals from 107 families with a deleterious TP53 variant, 403 cancer diagnoses were reported, of which 211 were the first primary cancer including two prostate cancers diagnosed after age 45 years. Prostate cancer was also reported in 4 of 61 men with a second primary cancer. In a Dutch case series of 180 families meeting either classic Li-Fraumeni syndrome (LFS) or Li-Fraumeni-like (LFL) family history criteria, a deleterious TP53 variant was identified in 24 families with one case of prostate cancer found in each group (LFS or LFL). Prostate cancer risks varied on the basis of the family history criteria with LFS (RR, 0.50; 95% CI, 0.01-3.00) and LFL (RR, 4.90; 95% CI, 0.10-27.00). In a French case series of 415 families with a deleterious TP53 variant, four prostate cancers were reported, with a mean age at diagnosis of 63 years (range, 57-71 y).
Germline TP53 pathogenic variants have also been identified in men with prostate cancer who have undergone tumor testing. A prospective case series of 42 men with either localized, biochemically recurrent, or metastatic prostate cancer unselected for cancer family history or age at diagnosis undergoing tumor-only somatic testing found that 2 of 42 men (5%) were found to have a suspected TP53 germline pathogenic variant.
Further evidence supports an association between prostate cancer and germline TP53 pathogenic variants,[72,73,74] although additional studies to clarify the association with this gene are warranted.
NBN, which is also known as NBS1 (Nijmegan breakage syndrome 1), has been investigated for a potential association with risk of prostate cancer. (Refer to Table 3 for information about case-control studies that have assessed NBN as a potential prostate cancer susceptibility gene.) A retrospective case series of 692 men with metastatic prostate cancer unselected for cancer family history or age at diagnosis found that 0.3% (2 of 692 men) had a NBN pathogenic variant.
EPCAM (epithelial cellular adhesion molecule) testing has been included in some multigene panels likely due to EPCAM variants silencing MSH2. Specific large genomic rearrangement variants at the 3' end of EPCAM, which lies near MSH2, induce methylation of the MSH2 promoter resulting in MSH2 protein loss. (Refer to the EPCAM section in the PDQ summary on Genetics of Colorectal Cancer for a more detailed discussion about EPCAM and Lynch syndrome.) Pathogenic variants in MSH2 that are associated with Lynch syndrome were found to be associated with increased risk of prostate cancer. (Refer to the Mismatch Repair Genes section of this summary for information about MSH2 and prostate cancer risk.) Thus far, studies ascertaining the spectrum of germline pathogenic variants in men with prostate cancer have not identified pathogenic variants in EPCAM.
Decisions about risk-reducing interventions for patients with an inherited predisposition to prostate cancer, as with any disease, are best guided by randomized controlled clinical trials and knowledge of the underlying natural history of the process. However, existing studies of screening for prostate cancer in high-risk men (men with a positive family history of prostate cancer and African American men) are predominantly based on retrospective case series or retrospective cohort analyses. Because awareness of a positive family history can lead to more frequent work-ups for cancer and result in apparently earlier prostate cancer detection, assessments of disease progression rates and survival after diagnosis are subject to selection, lead time, and length biases. (Refer to the PDQ Cancer Screening Overview summary for more information.) This section focuses on screening and risk reduction of prostate cancer among men predisposed to the disease; data relevant to screening in high-risk men are primarily extracted from studies performed in the general population.
Information is limited about the efficacy of commonly available screening tests such as the digital rectal exam (DRE) and serum prostate-specific antigen (PSA) in men genetically predisposed to developing prostate cancer. Furthermore, comparing the results of studies that have examined the efficacy of screening for prostate cancer is difficult because studies vary with regard to the cutoff values chosen for an elevated PSA test. For a given sensitivity and specificity of a screening test, the positive predictive value (PPV) increases as the underlying prevalence of disease rises. Therefore, it is theoretically possible that the PPV and diagnostic yield will be higher for the DRE and for PSA in men with a genetic predisposition than in average-risk populations.[1,2]
Most retrospective analyses of prostate cancer screening cohorts have reported PPV for PSA, with or without DRE, among high-risk men in the range of 23% to 75%.[2,3,4,5,6] Screening strategies (frequency of PSA measurements or inclusion of DRE) and PSA cutoff for biopsy varied among these studies, which may have influenced this range of PPV. Cancer detection rates among high-risk men have been reported to be in the range of 4.75% to 22%.[2,5,6] Most cancers detected were of intermediate Gleason score (5-7), with Gleason scores of 8 or higher being detected in some high-risk men. Overall, there is limited information about the net benefits and harms of screening men at higher risk of prostate cancer. In addition, there is little evidence to support specific screening approaches in prostate cancer families at high risk. Risks and benefits of routine screening in the general population are discussed in the PDQ Prostate Cancer Screening summary. On the basis of the available data, most professional societies and organizations recommend that high-risk men engage in shared decision-making with their health care providers and develop individualized plans for prostate cancer screening based on their risk factors. A summary of prostate cancer screening recommendations for high-risk men by professional organizations is shown in Table 10.
Level of evidence: 5
Screening in carriers ofBRCApathogenic variants
An international study that focused on prostate cancer screening in carriers of BRCA1/BRCA2 pathogenic variants versus noncarriers reported initial screening results. The study recruited 2,481 men (791 BRCA1 carriers, 531 BRCA1 noncarriers; 731 BRCA2 carriers, 428 BRCA2 noncarriers). A total of 199 men (8%) presented with PSA levels higher than 3.0 ng/mL, which was the study PSA cutoff for recommending a biopsy. The overall cancer detection rate was 36.4% (59 prostate cancers diagnosed among 162 biopsies). Prostate cancer by BRCA pathogenic variant status was as follows: BRCA1 carriers (n = 18), BRCA1 noncarriers (n = 10); BRCA2 carriers (n = 24), BRCA2 noncarriers (n = 7). Using published stage and grade criteria for risk classification, intermediate- or high-risk tumors were diagnosed in 11 of 18 BRCA1 carriers (61%), 8 of 10 BRCA1 noncarriers (80%), 17 of 24 BRCA2 carriers (71%), and 3 of 7 BRCA2 noncarriers (43%). The PPV of PSA with a biopsy threshold of 3.0 ng/mL was 48% in carriers of BRCA2 pathogenic variants, 33.3% in BRCA2 noncarriers, 37.5% in BRCA1 carriers, and 23.3% in BRCA1 noncarriers. Ninety-five percent of the men were white; therefore, the results cannot be generalized to all ethnic groups. Follow-up for this study is ongoing.
Level of evidence (screening in carriers of BRCA pathogenic variants): 3
Chemoprevention of Prostate Cancer With Finasteride and Dutasteride
The benefits, harms, and supporting data regarding the use of finasteride and dutasteride for the prevention of prostate cancer in the general population are discussed in the PDQ summary on Prostate Cancer Prevention.
Tumor Sequencing to Inform Germline Findings and Targeted Therapies in Prostate Cancer
Precision medicine efforts are under way in prostate cancer to identify targetable variants for improved responses to therapy. Tumor sequencing is a primary method to identify somatic variants for potential treatment. However, increasingly germline pathogenic variants are being identified from tumor sequencing, and are necessitating efforts to engage patients in genetic counseling for potential inherited cancer risk. Most of these efforts have involved metastatic prostate cancer. In particular, germline pathogenic variants in BRCA2, ATM, and DNA repair genes [15,16] have been identified at substantial rates in tumor sequencing of metastatic prostate cancer. Furthermore, clinical activity in response to targeted agents is being demonstrated in the metastatic prostate cancer setting, such as with poly (ADP-ribose) polymerase (PARP) inhibition.Table 11 describes these studies and results.
Overall, emerging studies report germline pathogenic variant rates of up to 12% primarily in metastatic prostate cancer, with the potential for clinical activity of PARP inhibitors for those with DNA repair pathogenic variants. A consideration is the use of various gene panels in assessing germline pathogenic variant rates across studies. Genetic counseling in the setting of tumor sequencing is also an emerging paradigm.
The purpose of this section is to describe current approaches to assessing and counseling patients about susceptibility to prostate cancer. Genetic counseling for men at increased risk of prostate cancer encompasses all of the elements of genetic counseling for other hereditary cancers. (Refer to the PDQ summary on Cancer Genetics Risk Assessment and Counseling for more information.) The components of genetic counseling include concepts of prostate cancer risk, reinforcing the importance of detailed family history, pedigree analysis to derive age-related risk, and offering participation in research studies to those individuals who have multiple affected family members.[1,2]Genetic testing for prostate cancer susceptibility is not available outside of the context of a research study. Families with prostate cancer can be referred to ongoing research studies; however, these studies will not provide individual genetic results to participants.
Prostate cancer will affect an estimated one in nine American men during their lifetime. Currently, evidence exists to support the hypothesis that approximately 5% to 10% of all prostate cancer is due to rare autosomal dominant prostate cancer susceptibility genes.[4,5] The proportion of prostate cancer associated with an inherited susceptibility may be even larger.[6,7,8] Men are generally considered to be candidates for genetic counseling regarding prostate cancer risk if they have a family history of prostate cancer. The Hopkins Criteria provide a working definition of hereditary prostate cancer families. The three criteria include the following:
Families need to fulfill only one of these criteria to be considered to have hereditary prostate cancer. One study investigated attitudes regarding prostate cancer susceptibility among sons of men with prostate cancer. They found that 90% of sons were interested in knowing whether there is an inherited susceptibility to prostate cancer and would be likely to undergo screening and consider genetic testing if there was a family history of prostate cancer; however, similar high levels of interest in genetic testing for other hereditary cancer syndromes have not generally been borne out in testing uptake once the clinical genetic test becomes available.
Risk Assessment and Analysis
Assessment of a man concerned about his inherited risk of prostate cancer should include taking a detailed family history; eliciting information regarding personal prostate cancer risk factors such as age, race, and dietary intake of fats and dairy products; documenting other medical problems; and evaluating genetics-related psychosocial issues.
Family history documentation is based on construction of a pedigree, and generally includes the following:
(Refer to the Documenting the family history section in the PDQ summary on Cancer Genetics Risk Assessment and Counseling for a more detailed description of taking a family history.)
Analysis of the family history generally consists of four components:
A number of studies have examined the accuracy of the family history of prostate cancer provided by men with prostate cancer. This has clinical importance when risk assessments are based on unverified family history information. In an Australian study of 154 unaffected men with a family history of prostate cancer, self-reported family history was verified from cancer registry data in 89.6% of cases. Accuracy of age at diagnosis within a 3-year range was correct in 83% of the cases, and accuracy of age at diagnosis within a 5-year range was correct in 93% of the cases. Self-reported family history from men younger than 55 years and reports about first-degree relatives had the highest degree of accuracy. Self-reported family history of prostate cancer, however, may not be reliably reported over time, which underscores the need to verify objectively reported prostate cancer diagnoses when trying to determine whether a patient has a significant family history.
The personal health and risk-factor history includes, but is not limited to, the following:
The most definitive risk factors for prostate cancer are age, race, and family history. The correlation between other risk factors and prostate cancer risk is not clearly established. Despite this limitation, cancer risk counseling is an educational process that provides details regarding the state of the knowledge of prostate cancer risk factors. The discussion regarding these other risk factors should be individualized to incorporate the patient's personal health and risk factor history. (Refer to the Risk Factors for Prostate Cancer section of this summary for a more detailed description of prostate cancer risk factors.)
The psychosocial assessment in this context might include evaluation of the following:
One study found that psychological distress was greater among men attending prostate cancer screening who had a family history of the disease, particularly if they also reported an overestimation of prostate cancer risk. Psychological distress and elevated risk perception may influence adherence to cancer screening and risk management strategies. Consultation with a mental health professional may be valuable if serious psychosocial issues are identified.
Multigene (panel) tests for variants in genes associated with prostate cancer susceptibility are currently available and are increasingly being used in the clinic. (Refer to the Multigene [Panel] Testing in Prostate Cancer section for more information.) Although routine genetic testing of high-risk prostate cancer patients for inherited variants associated with the disease is not standard, many centers are studying the clinical utility of germline genetic testing and counseling in these patients.
Research to date has included survey, focus group, and correlation studies on psychosocial issues related to prostate cancer risk. (Refer to the PDQ summary on Cancer Genetics Risk Assessment and Counseling for more information about psychological issues related to genetic counseling for cancer risk assessment.) Genetic testing for pathogenic variants in genes with some association with prostate cancer risk is now available and has the potential to identify those at increased risk of prostate cancer. Having an understanding of the motivations of men who may consider genetic testing for inherited susceptibility to prostate cancer can help clinicians and researchers anticipate interest in testing. Further, these data may inform the nature and content of counseling strategies for men and their families, including consideration of the risks, benefits, decision-making issues, and informed consent for genetic testing.
Knowledge about risk of prostate cancer is thought to be a factor influencing men's decisions to pursue prostate cancer screening and, possibly, genetic testing. A study of 79 African American men (38 of whom had been diagnosed with prostate cancer and the remainder who were unaffected but at high risk of prostate cancer) completed a nine-item telephone questionnaire assessing knowledge about hereditary prostate cancer. On a scale of 0 to 9, with 9 representing a perfect score, scores ranged from 3.5 to 9 with a mean score of 6.34. The three questions relating to genetic testing were the questions most likely to be incorrect. In contrast, questions related to inheritance of prostate cancer risk were answered correctly by the majority of subjects. Overall, knowledge of hereditary prostate cancer was low, especially concepts of genetic susceptibility, indicating a need for increased education. An emerging body of literature is now exploring risk perception for prostate cancer among men with and without a family history. Table 12 provides a summary of studies examining prostate cancer risk perception.
Study conclusions vary regarding whether first-degree relatives (FDRs) of prostate cancer patients accurately estimate their prostate cancer risk. Some studies found that men with a family history of prostate cancer considered their risk to be the same as or less than that of the average man.[5,6] Other factors, including being married, have been associated with higher prostate cancer risk perception. A confounder in prostate cancer risk perception was confusion between benign prostatic hyperplasia and prostate cancer.
Anticipated Interest in Genetic Testing for Risk of Prostate Cancer
A number of studies summarized in Table 13 have examined participants' interest in genetic testing, if such a test were available for clinical use. Factors found to positively influence the interest in genetic testing include the following:
Findings from these studies were not consistent regarding the influence of race, education, marital status, employment status, family history, and age on interest in genetic testing. Study participants expressed concerns about confidentiality of test results among employers, insurers, and family and stigmatization; potential loss of insurability; and the cost of the test. These concerns are similar to those that have been reported in women contemplating genetic testing for breast cancer predisposition.[11,12,13,14,15,16] Concerns voiced about testing positive for a pathogenic variant in a prostate cancer susceptibility gene included decreased quality of life secondary to interference with sex life in the event of a cancer diagnosis, increased anxiety, and elevated stress.
Overall, these reports and a study that developed a conceptual model to look at factors associated with intention to undergo genetic testing  have shown a significant interest in genetic testing for prostate cancer susceptibility despite concerns about confidentiality and potential discrimination. These findings must be interpreted cautiously in predicting actual prostate cancer genetic test uptake once testing is available. In both Huntington disease and hereditary breast and ovarian cancers, hypothetical interest before testing was possible was much higher than actual uptake following availability of the test.[24,25]
In a sample comprised of undiagnosed men with and without a prostate cancer-affected FDR, older age and lower education levels were associated with lower levels of prostate cancer-specific distress (as measured by the 11-item Prostate Cancer Anxiety Subscale of the Memorial Anxiety Scale for Prostate Cancer); higher distress was associated with having more urinary symptoms. In the same study, men with a prostate cancer-affected FDR who perceived their relative's cancer as more threatening and who had a relative deceased from the disease reported higher distress. In general, prostate cancer-specific distress levels were low for both groups of men.
Screening for Prostate Cancer in Individuals at Increased Familial Risk
The proportion of prostate cancers attributed to hereditary causes is estimated to be 5% to 10%, and the risk of prostate cancer increases with the number of blood relatives with prostate cancer and young age at onset of prostate cancer within families. There is considerable controversy in prostate cancer about the use of serum prostate-specific antigen (PSA) measurement and digital rectal exam for prostate cancer early detection in the general population, with different organizations suggesting significantly different screening algorithms and age recommendations. (Refer to the PDQ summary on Prostate Cancer Treatment for more information about prostate cancer in the general population and the Interventions section of this summary for more information about inherited prostate cancer susceptibility.) This variation is likely to add to patient and provider confusion about recommendations for screening by members of hereditary cancer families or FDRs of prostate cancer patients. Psychosocial questions of interest include what individuals at increased risk understand about hereditary risk, whether informational interventions are associated with increased uptake of prostate cancer screening behaviors, and what the associated quality-of-life implications of screening are for individuals at increased risk. Also of interest is the role of the primary care provider in helping those at increased risk identify their risk and undergo age- and family-history-appropriate screening.
In most cancers, the goal of improved knowledge of hereditary risk can be translated rather easily into a desired increase in adherence to approved and recommended (if not proven) screening behaviors. This is complicated for prostate cancer screening by the lack of clear recommendations for men in both high-risk and general populations. (Refer to the Screening section of this summary for more information.) In addition, controversy exists with regard to the value of early diagnosis of prostate cancer. This creates uncertainty for patients and providers and challenges the psychosocial factors related to screening behavior.
Several small studies have examined the behavioral correlates of prostate cancer screening at average and increased prostate cancer risk based on family history; these are summarized in Table 14. In general, results appear contradictory regarding whether men with a family history are more likely to be screened than those not at risk and whether the screening is appropriate for their risk status. Furthermore, most of the studies had relatively small numbers of subjects, and the criteria for screening were not uniform, making generalization difficult.