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This executive summary reviews the topics covered in this PDQ summary on the genetics of endocrine and neuroendocrine neoplasias, with hyperlinks to detailed sections below that describe the evidence on each topic.
Several hereditary syndromes involve the endocrine or neuroendocrine glands. Multiple endocrine neoplasia type 1 (MEN1), multiple endocrine neoplasia type 2 (MEN2), multiple endocrine neoplasia type 4 (MEN4), familial pheochromocytoma (PHEO) and paraganglioma (PGL) syndrome (FPPL), Carney-Stratakis syndrome (CSS), and familial nonmedullary thyroid cancer (FNMTC) are covered in this summary. Autosomal dominantly inherited pathogenic variants have been identified as the cause of most of these syndromes. PHEOs and PGLs may also be found in individuals with von Hippel-Lindau disease. (Refer to the PDQ summary on von Hippel-Lindau Disease for more information.)
MEN1, which is primarily associated with the development of parathyroid tumors and primary hyperparathyroidism, duodenopancreatic neuroendocrine tumors (NETs), and pituitary tumors, is caused by germline pathogenic variants in the MEN1 gene. The primary endocrine features of MEN2, which is subdivided into MEN2A and MEN2B, include medullary thyroid cancer (MTC); its precursor, C-cell hyperplasia; PHEO; and parathyroid adenomas and/or hyperplasia. MEN2 is caused by germline pathogenic variants in the RET gene. MEN4 is a rare syndrome with clinical features that overlap with the other MEN syndromes; the most common features are primary hyperparathyroidism and pituitary adenomas. MEN4 is caused by germline pathogenic variants in the CDKN1B gene. Both FPPL and CSS are caused by germline pathogenic variants in the SDH genes. PHEOs and PGLs commonly occur sporadically as well, although up to 33% of apparently sporadic PHEOs in individuals with no known family history and up to 40% of apparently sporadic PGLs have a recognizable germline pathogenic variant in one of the known PGL/PHEO susceptibility genes. Multifocal, locally aggressive gastrointestinal stromal tumors (GISTs) are also found in individuals with CSS. FNMTC is a polygenic disease with no single locus responsible for the majority of cases or easily identifiable phenotype and is likely modified by multiple low-penetrance alleles and environmental factors.
Regular surveillance is a mainstay in individuals found to have or be at risk of carrying a pathogenic variant in MEN1, RET, CDKN1B, or one of the SDH genes. Surveillance recommendations include regular screening for both endocrine and nonendocrine manifestations of disease.
Surgical management of pituitary and parathyroid tumors in MEN1 is based on disease presentation and management of symptoms of the organ. Surgical management of duodenopancreatic NETs of MEN1 is more specific to preventing disease progression.
The decision to operate on PHEOs and PGLs in MEN2 is based on hormonal hypersecretion and symptomatology. Treatment of MTC consists of surgical removal of the entire thyroid gland, including the posterior capsule, and central lymph node dissection. In addition, risk-reducing thyroidectomy has been shown to reduce the subsequent incidence of persistent or recurrent disease in MEN2 patients who had thyroidectomy earlier in life. The timing of risk-reducing thyroidectomy is guided by the risks associated with specific RET variants, although basal calcitonin levels may be used to determine the optimal timing of the procedure. MEN2-related parathyroid disease may also be treated surgically or with medical therapy in high-risk surgical patients.
Parathyroid and pituitary tumors associated with MEN4 are also managed surgically, in accordance with treatment for other familial syndromes such as MEN1.
FPPL-associated PHEOs and PGLs are also treated surgically. Preoperative management aimed at preventing catecholamine-induced complications of the surgery is common.
The mainstay of treatment for CSS-associated GISTs and PGLs is complete surgical resection of the tumor. The timing of the operation correlates with the presentation of the tumor.
Thyroid cancers associated with FNMTC are also managed surgically, commonly with a total thyroidectomy. Patients who undergo a total thyroidectomy must receive lifelong thyroid hormone replacement therapy.
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 and conditions described in this summary are found in the Online Mendelian Inheritance in Man (OMIM) catalog. Refer to OMIM for 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, particularly for differences that exist in the germline. 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.
There are several hereditary syndromes that involve endocrine or neuroendocrine glands, such as multiple endocrine neoplasia type 1 (MEN1), multiple endocrine neoplasia type 2 (MEN2), multiple endocrine neoplasia type 4 (MEN4), pheochromocytoma (PHEO), paraganglioma (PGL), Li-Fraumeni syndrome, familial adenomatous polyposis, and von Hippel-Lindau disease. This summary currently focuses on MEN1, MEN2, MEN4, familial PHEO and PGL syndrome, Carney-Stratakis (CSS) syndrome, and familial nonmedullary thyroid cancer (FNMTC). Li-Fraumeni syndrome, familial adenomatous polyposis, Cowden syndrome, and von Hippel-Lindau disease are discussed in the PDQ summaries on Genetics of Breast and Gynecologic Cancers; Genetics of Colorectal Cancer; and von Hippel-Lindau Disease.
The term multiple endocrine neoplasia is used to describe a group of heritable tumors of endocrine tissues that may be benign or malignant. They are typically classified into two main categories: MEN1 (also known as Wermer syndrome) and MEN2. Historically, MEN2 was further stratified into three subtypes based on the presence or absence of certain endocrine tumors in the individual or family: MEN2A, familial medullary thyroid cancer (FMTC), and MEN2B (which is sometimes referred to as MEN3). FMTC is now considered a subtype of MEN2A. MEN4 was described as a novel syndrome in humans in 2011, with the major characteristics including primary hyperparathyroidism and pituitary adenomas. MEN syndrome–associated tumors usually manifest themselves by overproduction of hormones, tumor growth, or both. (Refer to the MEN1, MEN2, and MEN4 sections of this summary for more information.)
PGLs and PHEOs are rare tumors arising from chromaffin cells, which have the ability to synthesize, store, and secrete catecholamines and neuropeptides. Either tumor may occur sporadically, as a manifestation of a hereditary syndrome, or as the sole tumor in familial PGL and PHEO syndrome. (Refer to the Familial PHEO and PGL Syndrome section of this summary for more information.)
Affected individuals with CSS have multifocal, locally aggressive gastrointestinal stromal tumors and multiple neck, intrathoracic, and intra-abdominal PGLs at relatively early ages.[3,4,5] Although similarly named, this syndrome is distinct from Carney Complex and Carney Triad. (Refer to the CSS section of this summary for more information.)
FNMTC is thought to account for 5% to 10% of all differentiated thyroid cancer cases.[6,7,8] With the exception of a few rare genetic syndromes with nonmedullary thyroid cancer as a minor component, most FNMTC is nonsyndromic, and the underlying genetic predisposition is unclear. (Refer to the FNMTC section of this summary for more information.)
Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant syndrome, with an estimated prevalence of about 1 in 30,000 individuals. The major endocrine features of MEN1 include the following:
A clinical diagnosis of MEN1 is made when an individual has two of these three major endocrine tumors. Familial MEN1 is defined as at least one MEN1 case plus at least one first-degree relative (FDR) with one of these three tumors, or two FDRs with a germline pathogenic variant.[2,3,4]
Initial clinical presentation of symptoms typically occurs between the ages of 20 years and 30 years, although a diagnosis of MEN1 may not be confirmed for many more years. The age-related penetrance of MEN1 is 45% to 73% by age 30 years, 82% by age 50 years, and 96% by age 70 years.[2,5,6]
Parathyroid Tumors and PHPT
The most common features and often the first presenting signs of MEN1 are parathyroid tumors, which result in PHPT. These tumors occur in 80% to 100% of patients by age 50 years.[7,8] Unlike the solitary adenoma seen in sporadic cases, MEN1-associated parathyroid tumors are typically multiglandular and often hyperplastic. The mean age at onset of PHPT in MEN1 is 20 to 25 years, in contrast to that in the general population, which is typically age 50 to 59 years. Parathyroid carcinoma in MEN1 is rare but has been described.[10,11,12]
Individuals with MEN1-associated PHPT will have elevated parathyroid hormone (PTH) and calcium levels in the blood. The clinical manifestations of PHPT are mainly the result of hypercalcemia. Mild hypercalcemia may go undetected and have few or no symptoms. More severe hypercalcemia can result in the following:
Since MEN1-associated hypercalcemia is directly related to the presence of parathyroid tumors, surgical removal of these tumors may result in normalization of calcium and PTH levels and relief of symptoms; however, high recurrence rates following surgery have been reported in some series.[13,14,15] (Refer to the Interventions section of this summary for more information.)
Duodenopancreatic NETs are the second most common endocrine manifestation in MEN1, occurring in 30% to 80% of patients by age 40 years.[2,7] A study has shown that the incidence may be as great as twofold higher in young patients (aged 20–40 y) with pathogenic variants in exon 2 of MEN1. These individuals are also more likely to have more aggressive disease and distant metastases. Furthermore, duodenopancreatic NETs are associated with early mortality even after surgical resection.
Duodenopancreatic NETs seen in MEN1 include the following:
Gastrinomas represent 50% of the gastrointestinal NETs in MEN1 and are the major cause of morbidity and mortality in MEN1 patients.[2,13] Gastrinomas are usually multicentric, with small (<0.5 cm) foci throughout the duodenum. Most result in peptic ulcer disease (Zollinger-Ellison syndrome), and half are malignant at the time of diagnosis.[13,21,22]
Nonfunctioning duodenopancreatic NETs were originally thought to be relatively uncommon tumors in individuals with MEN1. With the advent of genetic testing and improved imaging techniques, however, recognition of their prevalence in MEN1 has increased, with one study showing a frequency as high as 55% by age 39 years in carriers of MEN1 pathogenic variants undergoing prospective endoscopic ultrasonography of the pancreas.[19,23] These tumors can be metastatic. One study of 108 carriers of MEN1 pathogenic variants with nonfunctioning duodenopancreatic NETs showed a positive correlation between tumor size and rate of metastasis and death, with tumors larger than 2 cm having significantly higher rates of metastasis than those smaller than 2 cm. (Refer to the Molecular Genetics of MEN1 section of this summary for more information about MEN1gene pathogenic variants.)
Approximately 15% to 50% of MEN1 patients will develop a pituitary tumor.[2,7] Two-thirds are microadenomas (<1.0 cm in diameter), and the majority are prolactin-secreting. Other pituitary tumors can include somatotropinomas and corticotropinomas, or they may be nonfunctioning.
Other MEN1-Associated Tumors
Other manifestations of MEN1 include carcinoids of the foregut (5%–10% of MEN1 patients). These are typically bronchial or thymic and are sometimes gastric. Skin lesions are also common and can include facial angiofibromas (up to 80% of MEN1 patients) and collagenomas (~75% of MEN1 patients). Lipomas (~30% of MEN1 patients) and adrenal cortical lesions (up to 50% of MEN1 patients), including cortical adenomas, diffuse or nodular hyperplasia, or rarely, carcinoma are also common.[28,29,30] The following manifestations have also been reported:[31,32,33]
Making the Diagnosis of MEN1
MEN1 is often difficult to diagnose in the absence of a significant family history or a positive genetic test for a pathogenic variant in the MEN1 gene. One study of 560 individuals with MEN1 showed a significant delay between the time of the first presenting symptom and the diagnosis of MEN1. This time lapse is likely because some presenting symptoms of MEN1-associated tumors, such as amenorrhea, peptic ulcers, hypoglycemia, and nephrolithiasis, are not specific to MEN1.
Furthermore, identification of an MEN1-associated tumor is not sufficient to make the clinical diagnosis of MEN1 and may not trigger a referral to an endocrinologist. The median time between the first presenting symptom and diagnosis of MEN1 ranges from 7.6 years to 12 years.[5,29] Genetic testing alleviates some of this delay. Several studies have shown statistically significant differences in the age at MEN1 diagnosis between probands and their family members. In one study, clinically symptomatic probands were diagnosed with MEN1 at a mean age of 47.5 years (standard deviation [SD] +/- 13.5 y), while family members were diagnosed at a mean age of 38.5 years (SD +/- 15.4 y; P < .001). In another study of 154 individuals with MEN1, probands were diagnosed at a mean age of 39.5 years (range: 18–74 y), compared with a mean age of 27 years (range: 14–56 y; P < .05) in family members diagnosed by predictive genetic testing. Nonetheless, the lag time between the diagnosis of MEN1 in an index case and the diagnosis of MEN1 in family members can be significant, leading to increased morbidity and mortality. This was demonstrated in a Dutch MEN1 Study Group analysis, which showed that 10% to 38% of non-index cases already had an MEN1-related manifestation at diagnosis; 4% of these individuals died of an MEN1-related cause that developed during or before the lag time. In family members, the majority of the morbidity related to lag time was due to metastatic duodenopancreatic NETs, pituitary macroadenomas, and multiple MEN1 manifestations. Early intervention is particularly critical as it relates to mortality from duodenopancreatic NETs. A study showed that for every year older at time of surgery, the odds of metastasis increased by 6%. These findings underscore the importance of increased awareness of the signs and symptoms of MEN1-related tumors and the constellation of findings necessary to suspect the diagnosis. It also highlights the importance of genetic counseling and testing and communication among family members once a diagnosis of MEN1 is made.[37,38] Figure 1 illustrates some of the challenges in identifying MEN1 in a family.
Figure 1. MEN1 pedigree. MEN1 can be very difficult to identify in a pedigree. The pedigree on the left was constructed based on self-report, and the pedigree on the right depicts the same family following a review of available medical records. This pedigree shows some of the features of a family with an MEN1 pathogenic variant across four generations, including affected family members with hyperparathyroidism, a pituitary adenoma, gastrinoma, and a suspected pancreatic tumor. The tumors in MEN1 typically occur at an earlier age than their sporadic counterparts. MEN1 families may exhibit some or all of these features. As an autosomal dominant syndrome, transmission can occur through maternal or paternal lineages, as depicted in the figure.
Since many of the tumors in MEN1 are underdiagnosed or misdiagnosed, identifying an MEN1 gene pathogenic variant in the proband early in the disease process can allow for early detection and treatment of tumors and earlier identification of at-risk family members. Many studies have been performed to determine the prevalence of MEN1 gene pathogenic variants among patients with apparently sporadic MEN1-related tumors. For example, approximately one-third of patients with Zollinger-Ellison syndrome will carry an MEN1 pathogenic variant.[39,40] In individuals with apparently isolated PHPT or pituitary adenomas, the pathogenic variant prevalence is lower, on the order of 2% to 5%,[25,41,42] but the prevalence is higher in individuals diagnosed with these tumors before age 30 years. Some authors suggest referral for genetics consultation and/or genetic testing for pathogenic variants in MEN1 if one of the following conditions is present:[7,43,44]
Molecular Genetics of MEN1
The MEN1 gene is located on chromosome 11q13 and encodes the protein menin.[3,45,46] Over 1,300 pathogenic variants have been identified in the MEN1 gene to date, and these are scattered across the entire coding region.[47,48] Most (~65%) of these are nonsense or frameshift variants. The remainder are missense variants (20%), which lead to expression of an altered protein, splice-site variants (9%), or partial- or whole-gene deletions (1%–4%). Inter- and intra-familial variability is common.[7,49,50] One large study demonstrated the highest rates of heritability for pituitary, adrenal, and thymic NETs.
Genetic Testing and Differential Diagnosis
Genetic testing for MEN1 pathogenic variants is recommended for individuals meeting clinical diagnostic criteria and may be considered in a subset of the less common tumors. (Refer to the bulleted list in the Making the diagnosis of MEN1 section of this summary for more information.) For individuals meeting diagnostic criteria, the pathogenic variant detection rate is approximately 75% to 90%.[49,52] Still, germline pathogenic variant yield ranged from 16% to 38% for apparently sporadic cases of parathyroid (15.8%), pancreatic islet (25.0%), or pituitary (37.5%) tumors, warranting consideration of genetic testing in these individuals because a diagnosis of MEN1 would prompt screening for other MEN1-related tumors. Laboratories currently offering MEN1 testing use DNA sequencing as their primary method. Several offer additional analysis for partial- or whole-gene deletion and/or duplication, although such variants are rare and deletion/duplication testing is often reserved for individuals or families in which there is a very high clinical suspicion but no detectable pathogenic variant by direct sequencing.
A multigene panel that includes MEN1 and other genes associated with an increased risk of endocrine tumors may also be used. Such genetic testing can be used to distinguish between MEN1 and other forms of hereditary hyperparathyroidism, such as familial isolated hyperparathyroidism (FIHP), hyperparathyroidism–jaw tumor syndrome (HPT-JT), and familial hypocalciuric hypercalcemia (FHH). The hyperparathyroidism in FHH is not primary hyperparathyroidism, which is seen in MEN1, HPT-JT and FIHP. HPT-JT, which is caused by germline pathogenic variants in the HRPT2 gene, is associated with PHPT, ossifying lesions of the maxilla and mandible, and renal lesions, usually bilateral renal cysts, hamartomas, and in some cases, Wilms tumor.[54,55] Unlike MEN1, HPT-JT is associated with an increased risk of parathyroid carcinoma. FIHP, as its name suggests, is characterized by isolated PHPT with no additional endocrine features; in some families, FIHP is the initial diagnosis of what later develops into MEN1, HPT-JT, or FHH.[57,58,59] Approximately 20% of families with a clinical diagnosis of FIHP carry germline MEN1 pathogenic variants.[58,60,61] Pathogenic variants in the calcium-sensing receptor (CaSR) gene cause FHH, which can closely mimic the hyperparathyroidism in MEN1. Distinguishing between MEN1 and FHH can be critical in terms of management, as removal of the parathyroid glands in FHH does not correct the patient's hyperparathyroidism and results in unnecessary surgery without relief of symptoms. Given the differential risks and management of these conditions and the increased risk of parathyroid carcinoma in HPT-JT, genetic diagnosis in a patient presenting with early-onset hyperparathyroidism may play an important role in the management of these patients and their families. Refer to Table 3 for a summary of the clinical features of MEN1 and other forms of hereditary hyperparathyroidism.
Screening and surveillance for MEN1 may employ a combination of biochemical tests and imaging. Available recommendations are summarized in Table 4.[4,7]
Surgical management of MEN1 is complex and controversial, given the multifocal and multiglandular nature of the disease and the high risk of tumor recurrence even after surgery. Establishing the diagnosis of MEN1 before making surgical decisions and referring affected individuals to a surgeon with experience in treating MEN1 can be critical in preventing unnecessary operations or inappropriate surgical approaches.
Treatment for parathyroid tumors
Once evidence of parathyroid disease is established biochemically, the recommended course of action is surgical removal of the hyperfunctional parathyroid tissue. The timing and the extent of the operation, however, remain controversial. For patients with primary hyperparathyroidism who are at risk for MEN1, preoperative detection of a pathogenic variant helps guide the extent of surgery and can increase the likelihood of successful initial surgery and lower the likelihood of recurrent disease. Some groups reserve surgical intervention for symptomatic patients, with continued annual biochemical screening for those who are clearly asymptomatic. Once it is determined to proceed with surgery, subtotal parathyroidectomy (removal of 3–3.5 glands) is commonly suggested as the initial treatment. If 3.5 or more glands are removed, the rate of persistent disease is 5% to 6%. Preoperative imaging to determine which glands are hyperfunctional is not sufficiently reliable to justify unilateral exploration, with 86% of patients having enlarged contralateral parathyroid glands that were missed. Fifty percent of the patients who had imaging to direct resection had the largest parathyroid gland identified intraoperatively on the contralateral side of greatest uptake. Insufficient resection renders a patient to need reoperation.[13,14,15,63] Total parathyroidectomy with autotransplantation of parathyroid tissue to a distant site, such as the forearm, is also an option. A benefit of this approach is the easier removal or debulking of recurrent disease from the forearm than from the neck. This also allows for differential lateralization with arm blood draws. If total thyroidectomy is performed, the likelihood of recurrence is lowered but this must be weighed against the risk of rendering the patient hypoparathyroid or even aparathyroid (no detectable PTH in the body).[69,70] If the devastating complication of hypocalcemia occurs, management requires oral calcitriol and calcium supplementation. This daily drug dependence can be a major burden on patients. Studies showing that concomitant bilateral cervical thymectomy decreases the rate of recurrence suggest that the thymus be removed at the initial operation.
Treatment for duodenopancreatic NETs
The timing and extent of surgery for duodenopancreatic NETs are controversial and depend on many factors, including severity of symptoms, extent of disease, functional component, location and necessity of simple enucleation, subtotal or total pancreatectomy, and pancreaticoduodenectomy (Whipple procedure). Surgical enucleation has been associated with higher recurrence compared with distal pancreatectomy, and a decreased rate of endocrine insufficiency compared with a Whipple procedure. Tumor size has been suggested to advocate for surgical resection on the basis of the increased propensity for risk of metastases or recurrence with increased tumor diameter.[72,73] Unfortunately, there is no specific tumor marker or combination of tumor markers that are predictive of disease-specific mortality. Long-acting somatostatin analogs may have a role in early-stage MEN1 duodenopancreatic NETs. Initial study results of pharmacologic therapy suggest that the treatment is safe and that long-term suppression of tumor and hormonal activity can be seen in up to 10% of patients and stability of hormone hyperfunction in 80% of patients. The primary goal of surgery is to improve long-term survival by reducing symptoms associated with hormone excess and lowering the risk of distant metastasis. Surgery is commonly performed for most functional tumors and for nonfunctioning NETs when the tumor exceeds 2 to 3 cm because the likelihood of distant metastases is high.[73,76,77,78] Structural imaging modalities alone are suboptimal for predicting the malignant potential of duodenopancreatic NETs. However, a study found that screening MEN1 patients with fluorine F 18-fludeoxyglucose positron emission tomography–computed tomography (18F-FDG PET-CT) identified those NETs with an increased malignant potential; the FDG avidity correlated with a Ki-67 index. Tumor size does seem to influence patient survival, with patients with smaller tumors having increased survival after resection. While more-extensive surgical approaches (e.g., pancreatoduodenectomy) have been associated with higher cure rates and improved overall survival,[81,82,83] they also have higher rates of postoperative complications and long-term morbidity. Therefore, the risks and benefits should be carefully considered, and surgical decisions should be made on a case-by-case basis. With regard to open or laparoscopic approaches, in selected patients, pancreatic laparoscopic surgery appears to be safe and associated with a shorter length of stay and fewer complications.
Individuals with MEN1 who are diagnosed with NETs often have multiple tumors of various types throughout the pancreas and duodenum, some of which can be identified using magnetic resonance imaging or computed tomography (CT). Combining functional tracer accumulation with anatomic imaging improves tumor localization. Gallium Ga 68-DOTATATE positron emission tomography–CT demonstrates excellent sensitivity in mapping duodenopancreatic NET disease. This modality may guide the initial workup and appears to be superior to standard somatostatin octreotide, especially for lesions smaller than 10 mm.[86,87] Many tumors are too small to be detected using standard imaging techniques, and intra-arterial secretin stimulation testing and/or intraoperative ultrasonography may also be useful.[88,89] Preoperative assessment using a combination of various biochemical and imaging modalities, intraoperative assessment of tumor burden, and resolution of hormonal hyper-secretion are critical and, in some series, have been associated with higher cure rates and longer disease-free intervals.[88,89,90,91]
In the current era of effective treatment for hyperfunctional hormone excess states, most MEN1-related deaths are due to the malignant nature of duodenopancreatic NETs. A less common but important risk of death is from malignant thymic carcinoid tumors. Indicators of a poor MEN1 prognosis include elevated fasting serum gastrin, the presence of functional hormonal syndromes, liver or distant metastases, aggressive duodenopancreatic NET growth, large duodenopancreatic NET size, or the need for multiple parathyroidectomies. The most common cause of non-MEN1–related death in this patient cohort is from cardiovascular disease.
Other duodenopancreatic NETs
Glucagonomas, VIPomas, and somatostatinomas are rare but often have higher rates of malignancy than other duodenopancreatic NETs. These are often treated with aggressive surgery.
Medical management of insulinoma using diet and medication is often unsuccessful; the mainstay of treatment for this tumor is surgical resection. Insulinomas in MEN1 patients can be located throughout the pancreas, with a preponderance found in the distal gland,[94,95,96] and have a higher rate of metastasis than sporadic insulinoma. Surgery can range from enucleation of single or multiple large tumors to partial pancreatic resection, or both, to subtotal or total pancreatectomy.[94,95] More-extensive surgical approaches are associated with a lower rate of recurrence [81,82,95,97] but a higher rate of postoperative morbidity. Because insulinoma often occurs in conjunction with nonfunctioning pancreatic tumors, the selective intra-arterial calcium-injection test (SAS test) may be necessary to determine the source of insulin excess. Intraoperative monitoring of insulin/glucose can help determine whether insulin-secreting tumors have been successfully excised.[89,99]
Most MEN1-associated gastrinomas originate in the duodenum. These tumors are typically multifocal and cause hyper-secretion of gastrin, with resultant peptic ulcer disease (Zollinger-Ellison syndrome). The multifocal nature makes complete surgical resection difficult. It is critical to manage symptoms before considering any type of surgical intervention. Historically, some groups have recommended close observation of individuals with smaller tumors (<2.0 cm on imaging) who have relief of symptoms using medications (e.g., proton pump inhibitors or histamine-2 agonists); however, this approach may not be optimal for all patients.
Several published series have shown a positive correlation between primary tumor size and rate of distant metastasis. One retrospective study showed that 61% of patients with tumors larger than 3 cm had liver metastases. In another series, 40% of patients with tumors larger than 3 cm had liver metastases. In contrast, both of these series showed significantly lower rates of liver metastases in individuals with tumors smaller than 3 cm (32% and 4.8%, respectively). On the basis of these and other data, many groups recommend surgery in individuals with nonmetastatic gastrinoma who have tumors larger than 2 cm.[7,83]
The type of surgery for gastrinoma depends on many factors. A Whipple procedure is typically discouraged as an initial surgery, given the high postoperative morbidity and long-term complications, such as diabetes mellitus and malabsorption. Less extensive operations have been described with varying results. At a minimum, duodenectomy with intraoperative palpation and/or ultrasonography to locate and excise duodenal tumors and peri-pancreatic lymph node dissection are performed.[88,104] Because most patients with gastrinoma will have concomitant NETs throughout the pancreas, some of which may be nonfunctional, some groups recommend resection of the distal pancreas and enucleation of tumors in the pancreatic head in addition to duodenal tumor excision.[88,104,105]
Approximately 50% of individuals with MEN1 will develop nonfunctioning NETs.[19,24] These are often identified incidentally during assessment and exploration for functioning tumors. As with gastrinomas, the metastatic rate is correlated with larger tumor size.[24,73] Tumors smaller than 1.5 cm are not likely to have lymph node metastases, although the presence of metastatic disease has been associated with earlier age at death than in those without duodenopancreatic NETs.[8,24]
Medical therapy to suppress hypersecretion is often the first line of therapy for MEN1-associated pituitary tumors. In one series of 136 patients, medical therapy was successful in approximately one-half of patients with secreting tumors (49 of 116, 42%), and successful suppression was correlated with smaller tumor size. Surgery is often necessary for patients who are resistant to this treatment. Radiation therapy is reserved for patients for whom complete surgical resection was not rendered.[7,108]
The endocrine disorders observed in multiple endocrine neoplasia type 2 (MEN2) are medullary thyroid cancer (MTC); its precursor, C-cell hyperplasia (CCH) (referred to as C-cell neoplasia or C-cell carcinoma in situ in more recent publications); pheochromocytoma (PHEO); and parathyroid adenomas and/or hyperplasia. MEN2-associated MTC is often bilateral and/or multifocal and arises in the background of CCH clonal C-cell proliferation. In contrast, sporadic MTC is typically unilateral and/or unifocal. Because approximately 75% to 80% of sporadic cases also have associated CCH, this histopathologic feature cannot be used as a predictor of familial disease. Metastatic spread of MTC to regional lymph nodes (i.e., parathyroid, paratracheal, jugular chain, and upper mediastinum) or to distant sites, such as the liver, is common in patients who present with a palpable thyroid mass or diarrhea.[3,4] Metastatic PHEOs in MEN2 have not been reported. Parathyroid abnormalities in MEN2 can range from benign parathyroid adenomas or multigland hyperplasia to clinically evident hyperparathyroidism with hypercalcemia and renal stones.
Historically, individuals and families with MEN2 were classified into one of the following three clinical subtypes on the basis of the presence or absence of certain endocrine tumors in the individual or family:
Current stratification has moved away from a solely phenotype -based classification to one that is based on genotype (i.e., the pathogenic variant) and phenotype. Current classification now includes two MEN2 syndromes: MEN2A and MEN2B. The MEN2A syndrome is further classified on the basis of the presence of associated conditions. For example, classical MEN2A includes those with MTC, PHEO, and/or hyperparathyroidism. Additional categories include MEN2A with cutaneous lichen amyloidosis, MEN2A with Hirschsprung disease (HSCR), and FMTC (presence of a RETgermline pathogenic variant and MTC but no family history of PHEO or hyperparathyroidism). Classifying a patient or family by MEN2 subtype is useful in determining prognosis and management.
The prevalence of MEN2 has been estimated to be approximately 1 in 35,000 individuals. The vast majority of MEN2 cases are MEN2A.
MTC and CCH
MTC originates in calcitonin-producing cells (C-cells) of the thyroid gland. MTC is diagnosed when nests of C-cells extend beyond the basement membrane and infiltrate and destroy thyroid follicles. CCH is a controversial diagnosis, but most pathologists agree that it is defined as more than seven C-cells per cluster, complete follicles surrounded by C-cells, and C-cells in a distribution beyond normal anatomical location.[1,8,9,10] Individuals with RET pathogenic variants and CCH are at substantially increased risk of progressing to MTC. MTC and CCH are suspected in the presence of an elevated plasma calcitonin concentration.
A study of 10,864 patients with nodular thyroid disease found 44 (1 of every 250) cases of MTC after stimulation with calcitonin, none of which were clinically suspected. Consequently, half of these patients had no evidence of MTC on fine-needle biopsy and thus might not have undergone surgery without the positive calcitonin stimulation test. CCH associated with a positive calcitonin stimulation test occurs in about 5% of the general population; therefore, the plasma calcitonin responses to stimulation do not always distinguish CCH from small MTC and cannot always distinguish between carriers and noncarriers in an MEN2 family.[12,13,14]
MTC accounts for 1% to 2% of new cases of thyroid cancer diagnosed annually in the United States. Approximately 75% of thyroid cancer cases diagnosed in the United States are sporadic (i.e., they occur in the absence of a family history of either MTC or other endocrine abnormalities seen in MEN2). The peak incidence of the sporadic form is in the fifth and sixth decades of life.[3,16] A study in the United Kingdom estimated the incidence of MTC at 20 to 25 new cases per year among a population of 55 million.
In the absence of a positive family history, MEN2 may be suspected when MTC occurs at an early age or is bilateral or multifocal. While small series of apparently sporadic MTC cases have suggested a higher prevalence of germline RET pathogenic variants,[18,19] larger series indicate a prevalence range of 1% to 7%.[20,21] On the basis of these data, testing for pathogenic variants in the RETgene is widely recommended for all cases of MTC.[1,22]
Level of evidence (Screening): 3
Natural history of MTC
Thyroid cancer represents approximately 2.3% of new malignancies occurring annually in the United States, with an estimated 44,280 cancer diagnoses and 2,200 cancer deaths per year. Of these cancer diagnoses, 1% to 2% are MTC.
MTC arises from the parafollicular calcitonin-secreting cells of the thyroid gland. MTC occurs in sporadic and familial forms and may be preceded by CCH, although CCH is a relatively common abnormality in middle-aged adults.[8,9]
Average survival for MTC is lower than that for more common thyroid cancers (e.g., 86%–89% 5-year survival for MTC compared with 94%–98% 5-year survival for papillary and follicular thyroid cancer).[15,24] Survival is correlated with stage at diagnosis, and decreased survival in MTC can be accounted for in part by a high proportion of late-stage diagnosis.[25,26,27]
In addition to early stage at diagnosis, other factors associated with improved survival in MTC include smaller tumor size, younger age at diagnosis, and diagnosis by biochemical or genetic screening (i.e., screening for calcitonin elevation, RET variants) versus symptoms.[26,28,29,30]
A Surveillance, Epidemiology, and End Results population-based study of 1,252 MTC patients found that survival varied by extent of local disease. For example, the 10-year survival rates ranged from 95.6% for those with disease confined to the thyroid gland to 40% for those with distant metastases.
While most MTC cases are sporadic, approximately 20% to 25% are hereditary because of pathogenic variants in the RET proto-oncogene. Pathogenic variants in the RET gene cause MEN2, an autosomal dominant disorder associated with a high lifetime risk of MTC. Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant endocrinopathy that is genetically and clinically distinct from MEN2; however, the similar nomenclature for MEN1 and MEN2 may cause confusion. There is no increased risk of thyroid cancer for MEN1. (Refer to the MEN1 section of this summary for more information.)
PHEOs arise from the catecholamine-producing chromaffin cells of the adrenal medulla. They are relatively rare tumors and are suspected among patients with refractory hypertension or when biochemical screening reveals elevated excretion of catecholamines and catecholamine metabolites (i.e., norepinephrine, epinephrine, metanephrine, and vanillylmandelic acid) in 24-hour urine collections or plasma. In the past, measurement of urinary catecholamines was considered the preferred biochemical screening method. However, given that catecholamines are only released intermittently and are metabolized in the adrenal medulla into metanephrine and normetanephrine, the measurement of urine or plasma fractionated metanephrines has become the gold standard.[32,33,34,35,36,37] When biochemical screening in an individual who has or is at risk of MEN2 suggests PHEO, localization studies, such as magnetic resonance imaging (MRI) or computed tomography, can be performed. Confirmation of the diagnosis can be made using iodine I 131-metaiodobenzylguanidine scintigraphy or positron emission tomography imaging.[13,38,39,40]
For individuals with PHEO, a diagnosis of MEN2 is often considered in individuals with bilateral disease, those with an early age of onset (age <35 y), and those with a personal and/or family history of MTC or hyperparathyroidism. However, MEN2 is not the only genetic disorder that includes a predisposition to PHEO. Other disorders include neurofibromatosis type 1 (NF1), von Hippel-Lindau disease (VHL), and the hereditary paraganglioma syndromes. (Refer to the Familial PHEO and PGL Syndrome section of this summary for more information about hereditary PHEO and the PDQ summary on von Hippel-Lindau Disease for more information about VHL.)
Primary Hyperparathyroidism (PHPT)
PHPT is the third most common endocrine disorder in the general population. The incidence increases with age with the vast majority of cases occurring after the sixth decade of life. Approximately 80% of cases are the result of a single adenoma. PHPT can also be seen as a component tumor in several different hereditary syndromes, including the following:
Hereditary PHPT is typically multiglandular, presents earlier in life, and can have histologic evidence of both adenoma and glandular hyperplasia.
Clinical Diagnosis of MEN2 Subtypes
The diagnosis of the two MEN2 clinical subtypes relies on a combination of clinical findings, family history, and molecular genetic testing of the RET gene.
MEN2A is diagnosed clinically by the occurrence of two specific endocrine tumors in addition to MTC: PHEO and/or parathyroid adenoma and/or hyperplasia in a single individual or in close relatives.
The classical MEN2A subtype makes up about 60% to 90% of MEN2 cases. The MEN2A subtype was initially called Sipple syndrome. Since genetic testing for RET pathogenic variants has become available, it has become apparent that about 95% of individuals with MEN2A will develop MTC.[13,48,49,50]
MTC is generally the first manifestation of MEN2A. In asymptomatic at-risk individuals, stimulation testing may reveal elevated plasma calcitonin levels and the presence of CCH or MTC.[13,49] In families with MEN2A, the biochemical manifestations of MTC generally appear between the ages of 5 years and 25 years (mean, 15 y). If presymptomatic screening is not performed, MTC typically presents as a neck mass or neck pain between the ages of about age 5 years and 20 years. More than 50% of such patients have cervical lymph node metastases. Diarrhea, the most frequent systemic symptom, occurs in patients with a markedly elevated plasma calcitonin level or bulky disease and/or hepatic metastases and implies a poor prognosis.[1,3,51,52] Up to 30% of patients with MTC present with diarrhea and advanced disease.
MEN2-associated PHEOs are more often bilateral, multifocal, and associated with extratumoral medullary hyperplasia.[54,55,56] They also have an earlier age of onset and are less likely to be malignant than their sporadic counterparts.[54,57] MEN2-associated PHEOs usually present after MTC, typically with intractable hypertension.
Unlike the PHPT seen in MEN1, hyperparathyroidism in individuals with MEN2 is typically asymptomatic or associated with only mild elevations in calcium.[53,59] A series of 56 patients with MEN2-related hyperparathyroidism has been reported by the French Calcitonin Tumors Study Group. The median age at diagnosis was 38 years, documenting that this disorder is rarely the first manifestation of MEN2. This is in sharp contrast to MEN1, in which the vast majority of patients (87%–99%) initially present with primary hyperparathyroidism.[60,61,62] Parathyroid abnormalities were found concomitantly with surgery for medullary thyroid cancer in 43 patients (77%). Two-thirds of the patients were asymptomatic. Among the 53 parathyroid glands removed surgically, there were 24 single adenomas, 4 double adenomas, and 25 hyperplastic glands.
MEN2A with cutaneous lichen amyloidosis
A small number of families with MEN2A have pruritic skin lesions known as cutaneous lichen amyloidosis. This lichenoid skin lesion is located over the upper portion of the back and may appear before the onset of MTC.[63,64]
MEN2A with Hirschsprung disease (HSCR)
HSCR, a disorder of the enteric plexus of the colon that typically results in enlargement of the bowel and constipation or obstipation in neonates, occurs in a small number of individuals with MEN2A-associated RET pathogenic variants. Pathogenic variants at specific cysteine residues in exon 10 (i.e., codons 609, 618, and 620) are most commonly associated with HSCR, although individuals with pathogenic variants in other exons can still be affected. HSCR can occur outside of a diagnosis of MEN2A and infants with HSCR may benefit from their own genetic evaluation regardless of the likelihood of MEN2A because HSCR can present as part of other syndromes. Up to 40% of familial cases of HSCR and 3% to 7% of sporadic cases are associated with germline pathogenic variants in the RET proto-oncogene.[67,68] Certain loss-of-function RET variants have been associated with isolated HSCR, indicating that not all individuals with HSCR and a germline RET variant necessarily have MEN2A.
Figure 2 depicts some of the classic manifestations of MEN2A in a family.
Figure 2. MEN2A pedigree. This pedigree shows some of the classic features of a family with a RET pathogenic variant across four generations, including affected family members with medullary thyroid cancer, pheochromocytoma, and hyperparathyroidism. Age at onset can vary widely, even within families. MEN2A families may exhibit some or all of these features. As an autosomal dominant syndrome, transmission can occur through maternal or paternal lineages.
Familial medullary thyroid cancer (FMTC)
Up to 50% of MEN2A cases are of the FMTC subtype, and are defined as families or single individuals with germline RET pathogenic variants and MTC alone in the absence of PHEO or parathyroid adenoma/hyperplasia. This definition replaces previous classification of FMTC as a stand-alone diagnosis. Previously, misclassification of families as having FMTC (because of too-small family size or later onset of other manifestations of MEN2A) could result in overlooking the risk of PHEO, a disease with significant morbidity and mortality. For this reason, FMTC is now considered a subtype of MEN2A in which there is a lack of or delay in the onset of the other (nonthyroidal) manifestations of the MEN2A syndrome. Current management guidelines  recommend that patients thought to have pure FMTC also be screened for PHEO and hyperparathyroidism.
MEN2B is diagnosed clinically by the presence of mucosal neuromas of the lips and tongue, medullated corneal nerve fibers, distinctive facies with enlarged lips, an asthenic Marfanoid body habitus, and MTC.[71,72,73,74] In cases of de novo pathogenic variants, the diagnosis of MEN2B is often delayed, after the development of MTC. The MTC is often fatal, particularly in the presence of metastatic disease, which is common at the time of diagnosis. It is important, therefore, for pediatricians to recognize the endocrine and nonendocrine clinical manifestations of the syndrome as an earlier diagnosis may result in lifesaving treatment of MTC, before metastatic spread.
The MEN2B subtype makes up about 5% of MEN2 cases. The MEN2B subtype was initially called mucosal neuroma syndrome or Wagenmann-Froboese syndrome. MEN2B is characterized by the early development of an aggressive form of MTC in all patients. Patients with MEN2B who do not undergo thyroidectomy at an early age (at approximately age 1 y) are likely to develop metastatic MTC at an early age. Before intervention with early risk-reducing thyroidectomy, the average age at death in patients with MEN2B was 21 years. PHEOs occur in about 50% of MEN2B cases; about half are multiple and often bilateral. Clinically apparent parathyroid disease is very uncommon.[48,71] Patients with MEN2B may be identified in infancy or early childhood by a distinctive facial appearance and the presence of mucosal neuromas on the anterior dorsal surface of the tongue, palate, or pharynx. The lips become prominent over time, and submucosal nodules may be present on the vermilion border of the lips. Neuromas of the eyelids may cause thickening and eversion of the upper eyelid margins. Prominent thickened corneal nerves may be seen by slit lamp examination.
Patients with MEN2B may have diffuse ganglioneuromatosis of the gastrointestinal tract with associated symptoms that include abdominal distension, megacolon, constipation, and diarrhea. A review of the literature reported the presence of constipation as a common symptom in 72.7% of patients with MEN2B. Additionally, gastrointestinal symptoms occurred during the first year of life in 52.3% of patients with MEN2B. Intestinal biopsy led to the diagnosis of ganglioneuromatosis in 27.3% of patients.
About 75% of patients have a Marfanoid habitus, often with kyphoscoliosis or lordosis, joint laxity, and decreased subcutaneous fat. Proximal muscle wasting and weakness can also be seen.[73,74]
A retrospective review of the clinical presentation of 35 cases of MEN2B with de novo pathogenic variants treated at a single institution found that 22 cases were diagnosed because of endocrine manifestations of the syndrome. The diagnosis of PHEO, a neck mass, and/or skeletal abnormalities led to the identification of MTC. The remaining 13 patients presented with a nonendocrine manifestation, including oral neuromas, corneal nerve abnormalities, persistent diarrhea, failure to thrive, or skeletal abnormalities with frequent falls. Of the entire cohort, 21 patients had one or more physician referrals for the evaluation of an MEN2B-related feature, an average of 5 years before the diagnosis of MEN2B.
It is critical for pediatricians to maintain a high index of suspicion when evaluating patients with any of the clinical manifestations associated with MEN2B. In a child, the presence of oral and ocular neuromas and/or a tall and lanky appearance may warrant further investigation. Some authors have recommended referral to genetic counseling for an individual with MTC or any of the following features:[71,79]
Molecular Genetics of MEN2
MEN2 syndromes are the result of inherited pathogenic variants in the RET gene, located on chromosome region 10q11.2.[80,81,82] The RET gene is a proto-oncogene composed of 21 exons over 55 kilobase of genomic material.[83,84]
RET encodes a receptor tyrosine kinase with extracellular, transmembrane, and intracellular domains. Details of RET receptor and ligand interaction in this signaling pathway have been reviewed.[31,85,86] Briefly, the extracellular domain consists of a calcium-binding cadherin-like region and a cysteine-rich region that interacts with one of four ligands identified to date. These ligands, e.g., glial cell line–derived neurotrophic factor (GDNF), neurturin, persephin, and artemin, also interact with one of four coreceptors in the GDNF-family receptor–alpha family. The tyrosine kinase catalytic core is located in the intracellular domain, which causes downstream signaling events through a variety of second messenger molecules.
MEN2 is a well-defined hereditary cancer syndrome for which genetic testing is considered an important part of the management for at-risk family members. It meets the criteria related to indications for genetic testing for cancer susceptibility outlined by the American Society of Clinical Oncology in its most recent genetic testing policy statement. At-risk individuals are defined as first-degree relatives (parents, siblings, and children) of a person known to have MEN2. Testing allows the identification of people with asymptomatic MEN2 who can be offered risk-reducing thyroidectomy and biochemical screening as preventive measures. A negative pathogenic variant analysis in at-risk relatives, however, is informative only after a disease-causing variant has been identified in an affected relative. (Refer to the PDQ summary on Cancer Genetics Risk Assessment and Counseling for more information.) Because early detection of at-risk individuals affects medical management, testing of children who have no symptoms is considered beneficial.[88,89] (Refer to the Genotype-Phenotype Correlations and Risk Stratification section of this summary for more information about clinical management of at-risk individuals.)
Germline DNA testing for RET pathogenic variants is generally recommended to all individuals with a diagnosis of MTC, regardless of whether there is a personal or family history suggestive of MEN2.[90,91] Approximately 95% of patients with MEN2A or MEN2B will have an identifiable germline RET pathogenic variant. Between 1% and 10% of individuals with apparently sporadic MTC will carry a germline RET pathogenic variant, underscoring the importance of testing all individuals diagnosed with MTC.[93,94,95]
There is no evidence for the involvement of other genetic loci, and all pathogenic variant–negative families analyzed to date have demonstrated linkage to the RET gene. For families that do not have a detectable pathogenic variant, clinical recommendations can be based on the clinical features in the affected individual and in the family.
There is considerable diversity in the techniques used and the approach to RET pathogenic variant testing among the various laboratories that perform this procedure. Methods used to detect variants in RET include polymerase chain reaction (PCR) followed by restriction enzyme digestion of PCR products, heteroduplex analysis, single-stranded conformation polymorphism analysis, denaturing high-performance liquid chromatography, and DNA sequencing.[92,96] Most testing laboratories, at a minimum, offer testing using a targeted exon approach; that is, the laboratories look for variants in the exons that are most commonly found to carry variants (exons 10, 11, 13, 14, 15 and 16). Other laboratories offer testing for all exons. If targeted exon testing in a family with a high clinical suspicion for MEN2 is normal, sequencing of the remaining exons can then be performed.
These differences in variant detection method and targeted versus full gene testing represent important considerations for selecting a laboratory to perform a test and in interpreting the test result. (Refer to the PDQ summary on Cancer Genetics Risk Assessment and Counseling for more information about clinical validity.)
Genotype-Phenotype Correlations and Risk Stratification
Genotype-phenotype correlations in MEN2 are well-established and have long been used to guide clinicians in making medical management recommendations. Several groups have developed pathogenic variant–stratification tables based on clinical phenotype, age of onset, and aggressiveness of MTC.[1,90,97] This classification strategy was first put forth after the Seventh International Workshop on MEN in 2001, which provided guidelines for the age of genetic testing and prophylactic thyroidectomy. This stratification has been revised by the American Thyroid Association (ATA).[1,98,99] The specific pathogenic variants and their ATA classification are summarized in Table 5 below.
ATA-Highest Risk (HST) (previously labeled ATA-D) pathogenic variants are the most aggressive and carry the highest risk of developing MTC. This category includes those with MEN2B and RET codon M918T pathogenic variants and is associated with the youngest age at disease onset and the highest risk of mortality. ATA-High Risk (H) (previously called ATA-C) pathogenic variants, at codons 634 and A883F, are associated with a slightly lower risk, yet the MTC in patients with these pathogenic variants is still quite aggressive and may present at an early age. Former ATA-levels A and B pathogenic variants are now combined into a single group called Moderate Risk (MOD) and are associated with a lower risk of aggressive MTC relative to the risk seen in carriers of ATA-HST and ATA-H pathogenic variants. Results from a study of 387 RET pathogenic variant carriers with MTC have suggested that ATA-MOD variants may be associated with MTC as aggressive as seen in individuals with ATA-H variants but present at a later age. The risk of MTC is still substantially elevated over the general population risk and consideration of risk-reducing thyroidectomy is warranted. Patients with early stage I and stage II disease can achieve 100% survival rates regardless of the ATA risk category. Common pathogenic variants in the ATA-MOD category are shown in Table 5.
Pathogenic variants at codons 883 and 918 have been seen only in MEN2B and are associated with the earliest age of onset and the most aggressive form of MTC.[100,102,103,104,105,106] Approximately 95% of individuals with MEN2B will have the M918T pathogenic variant.[102,103,104,107] As discussed above, 50% of individuals with MEN2B will develop PHEO but PHPT is rare. A retrospective review of all published cases of A883F variant carriers (N = 13) found that the MTC disease course was more indolent than what was observed in M918T carriers. A883F carriers had later disease onset (50% penetrance for MTC at age 19 y), 5- and 10-year survival rates of 88%, and 63% of patients achieved biochemical cure for MTC. In addition to variants at codons 883 and 918, some individuals with an MEN2B-like phenotype have been found to carry two germline variants.[108,109,110,111,112] It is likely that as testing for RET becomes more common in clinical practice, additional double variant phenotypes will be described.
Pathogenic variants at codon 634 (ATA-H) are by far the most frequent finding in families with MEN2A. One study of 477 RET carriers showed that 52.1% had the C634R pathogenic variant, 26.0% carried the C634Y pathogenic variant, and 9.1% had the C634G pathogenic variant. In general, pathogenic variants at codon 634 are associated with PHEOs and PHPT.[48,113] Until recently, MEN2A with cutaneous lichen amyloidosis had been seen almost exclusively in patients with pathogenic variants at codon 634.[48,50,114] However, a recent report described MTC and cutaneous lichen amyloidosis in an individual previously thought to have FMTC due to a codon 804 pathogenic variant. Codon 634 pathogenic variants have also been described in FMTC but are almost exclusively C634Y.
In summary, ATA-HST and ATA-H (previously levels D and C, respectively) pathogenic variants confer the highest risk of MTC (about 95% lifetime risk) with a more aggressive disease course. There is an increased risk of PHEO (up to 50%).[48,116] Individuals with codon 634 pathogenic variants (but not codon 883 or 918 variants) also have an increased risk of PHPT.
Moderate-risk variants located in exon 10 of the RET gene include variants at codons 609, 611, 618, 620, and 630. These variants involve cysteine residues in the extracellular domain of the RET protein and have been seen in families with MEN2A and those with MTC only (FMTC).[20,48,97,117,118,119,120,121] The risk of MTC in individuals with these pathogenic variants is approximately 95% to 100%; the risk of PHEO and hyperparathyroidism is lower than that seen in individuals with high-risk pathogenic variants.
Individuals with pathogenic variants previously classified as ATA-level A (now classified with ATA-level B as ATA-MOD, i.e., codons 321, 515, 533, 600, 603, 606, 531/9 base pair duplication, and 532 duplication) have a lower, albeit still elevated, lifetime risk of MTC. MTC associated with these pathogenic variants tends to follow a more indolent course and have a later age at onset, although there are several reports of individuals with these pathogenic variants who developed MTC before age 20 years.[48,122,123,124,125,126] Although PHEO and PHPT are not commonly associated with these pathogenic variants, they have been described.
In addition to the pathogenic variants categorized in Table 5, a number of rare or novel RET variants have been described. Some of these represent pathogenic variants that lead to MEN2A phenotypes. Others may represent low-penetrance alleles or modifying alleles that confer only a modest risk of developing MTC. A multicenter study identified eight families with a RET K666N variant. Of the 16 screened family members identified as having a pathogenic variant, only one had MTC. Still others may be benign polymorphisms of no clinical significance. For example, some studies demonstrate compelling evidence that RET variants Y791F (p.Tyr791Phe) and S649L (p.Ser649Leu) are likely benign polymorphisms, on the basis of equal frequencies among cases and healthy controls and co-occurrence with other disease-causing variants that cosegregate with disease in the family.[128,129] A long-term follow-up study of Danish Y791F carriers (n = 20) showed no sign of MEN2A (MTC, PHPT, PHEO, cutaneous lichen amyloidosis, or HSCR) among the cohort, with a median age of 49.5 years (range, 7–87 y). Therefore, carriers of these variants are not treated as having MEN2 syndrome and asymptomatic family members are generally not tested for these variants. Comprehensive testing of all hotspot variants in exons 8 and 10–16 may be performed to rule out any other RET pathogenic variants, and more extensive testing of other disease-related genes may be warranted because of a diagnosis of PHEO. (Refer to the Familial Pheochromocytoma and Paraganglioma Syndrome section of this summary for more information.)
Research is ongoing into the role of neutral RET sequence variants in modifying the clinical presentation of patients with MEN2A. The presence of certain RET polymorphisms or haplotypes is being analyzed for its impact on the likelihood for development of PHEO, hyperparathyroidism, HSCR, and age at onset of metastatic involvement with MTC.[131,132,133,134] A variety of approaches, including segregation analyses, in silico analyses, association studies, and functional assays, can be employed to determine the functional and clinical significance of a given genetic variant. A publicly available RET variant online database repository was developed and includes a complete list of variants and their associated pathogenicity, phenotype, and other associated clinical information and literature references.
Screening at-risk individuals for PHEO
The presence of a functioning PHEO can be excluded by appropriate biochemical screening before thyroidectomy in any patient with MEN2A or MEN2B. However, childhood PHEOs are rare in MEN2. The ATA recommends that annual screening for PHEO be considered by age 11 years in patients with ATA-HST or ATA-H RET pathogenic variants. The ATA recommends that patients with ATA-MOD RET pathologic variants have periodic screening for PHEO beginning by age 16 years. MRI or other imaging tests may be ordered only if the biochemical results are abnormal.[26,136] Studies of individuals with sporadic or hereditary PHEO (including, but not limited to, individuals with MEN2) have suggested that measurement of catecholamine metabolites, specifically plasma-free metanephrines and/or urinary fractionated metanephrines, provides a higher diagnostic sensitivity than urinary catecholamines because of the episodic nature of catecholamine excretion.[32,33,34,35,36,37,38,137] Several reviews provide a succinct summary of the biochemical diagnosis, localization, and management of PHEO.[38,138] In addition to surgery, there are other clinical situations in which patients with catecholamine excess face special risk. An example is the healthy at-risk female patient who becomes pregnant. Pregnancy, labor, or delivery may precipitate a hypertensive crisis in persons who carry an unrecognized PHEO. Pregnant patients who are found to have catecholamine excess require appropriate pharmacotherapy before delivery.
Level of evidence: 5
Screening at-risk individuals for hyperparathyroidism
MEN2-related hyperparathyroidism is generally associated with mild, often asymptomatic hypercalcemia early in the natural history of the disease, which, left untreated, may become symptomatic. Childhood hyperparathyroidism is rare in MEN2. Three studies found the median age at diagnosis was about 38 years.[59,139,140] The ATA provides recommendations for annual screening for hyperparathyroidism, with screening beginning by age 11 years in carriers of ATA-HST and ATA-H pathogenic variants and by age 16 years for carriers of ATA-MOD RET pathogenic variants. Testing typically includes albumin-corrected calcium or ionized serum calcium with or without intact parathyroid hormone (PTH) measurement.
Screening at-risk individuals in kindreds without an identifiableRETpathogenic variant
Risk-reducing thyroidectomy is not routinely offered to at-risk individuals unless MEN2A is confirmed. The screening protocol for MTC in patients with MEN2A is annual calcitonin stimulation test; however, caution must be used in interpreting test results because CCH that is not a precursor to MTC occurs in about 5% of the population.[12,13,141] In addition, there is significant risk of false-negative test results in patients younger than 15 years. Screening for PHEO and parathyroid disease is the same as described above.
For patients at risk of FMTC, annual screening for MTC is the same as for patients with MEN2A.
Treatment for MTC
Risk-reducing thyroidectomy is the oncologic treatment of choice for patients with MEN2. Children with the M918T RET pathogenic variant may benefit from a thyroidectomy in the first year of life, perhaps in the first months of life. Likewise, children with ATA-H category RET pathogenic variants may undergo prophylactic thyroidectomy at age 5 years or earlier, on the basis of serum calcitonin levels. The ATA recommends that children in the ATA-MOD category have a physical examination, ultrasonography of the neck, and measurement of the serum calcitonin beginning around age 5 years as these tumors may have later onset but are similarly aggressive once this is taken into account.[1,99] The absence of an abnormal calcitonin level may prompt continued measurement every 6 to 12 months.
A multidisciplinary team caring for the patient, including the pediatrician, pediatric endocrinologist, and surgeon should determine the timing of surgery in conjunction with the child's parents on the basis of the trend in serum calcitonin levels, ultrasonographic findings, preference of the family, and experience of the treating physicians.
In children with some ATA-H or ATA-MOD RET pathogenic variants, some studies have suggested that basal and pentagastrin-stimulated calcitonin levels could be used to determine the timing of total thyroidectomy.[142,143,144,145] These findings suggest that surgery may be safely delayed in carriers of an RET pathogenic variant until basal or stimulated calcitonin levels increase on routine testing. The benefits of this approach are particularly noteworthy in the younger population of pathogenic variant carriers, as a delay in surgery until the patient is older may reduce the risk of surgical complications. A large study of 2,740 children aged 16 years and under has provided data on age-specific reference ranges for calcitonin levels in younger children that may assist in decision making. Because some calcitonin assays may be more sensitive than others, attention to the type of testing, as well as calcitonin levels will need to be considered. However, normal preoperative basal calcitonin does not exclude the possibility of the patient having MTC.
For patients with RET germline variants, older age at prophylactic thyroidectomy has been significantly associated with a higher risk of postoperative persistent or recurrent disease. Consistent with this, a study of young, clinically asymptomatic individuals with MEN2A showed there was a lower incidence of persistent or recurrent disease in patients who had thyroidectomy earlier in life (defined as younger than age 8 y) and who had no evidence of lymph node metastases. Several studies have shown that there is a significantly lower rate of invasive or metastatic MTC among those who undergo surgery at an earlier age than among those who undergo surgery at a later age. For patients with the most aggressive M918T RET variant, cure is exceptional if surgery is performed after age 4 years.[142,151] Together, these findings are consistent with more favorable outcomes for patients undergoing early risk-reducing surgery.[150,152,153]
Although thyroidectomy before biochemical evidence of disease (normal preoperative calcitonin) may reduce the risk of recurrent disease, a selective strategy for postoperative and lifelong surveillance might depend on the final pathologic determination of whether a carcinoma was present and whether it was micromedullary or macromedullary.[1,154] One study found that 10% of patients with MEN2A undergoing thyroidectomy developed recurrent disease, on the basis of initially undetectable basal and stimulated calcitonin levels (<2 pg/mL) that became positive 5 to 10 years after surgery. Only 2% of patients had residual disease after prophylactic surgery as assessed by a persistently elevated basal or stimulated calcitonin.
Questions remain concerning the natural history of MEN2. As more information is acquired, recommendations regarding the optimal age for thyroidectomy and the potential role for genetics and biochemical screening may change. Earliest reports of MTC in MEN2B before age 3 years, and before age 6 years in MEN2A cases with ATA-H or ATA-MOD RET variants have been documented.[142,149,151,155] Conversely, another case report documented onset of cancer in midlife or later in some families with the FMTC subtype of MEN2A and in elderly relatives who carry the RET variant genotype but have not developed cancer. Subsequent data have suggested that some ATA-MOD RET variants, which were previously thought of as more indolent may be as aggressive as ATA-H variants, but are associated with delayed onset of disease.[99,101] Emerging data pertaining to the timing of disease onset and local metastases by risk category are evolving. These clinical observations suggest that the natural history of the MEN2 syndromes is variable and could be subject to modifying effects related to specific RET pathogenic variants, other genes, behavioral factors, or environmental exposures.
Level of evidence: 4b
The standard treatment for adults with MTC is surgical removal of the entire thyroid gland, including the posterior capsule and central lymph node dissection. A therapeutic central neck dissection is typically performed if there is radiographic evidence of metastatic lymph node involvement or if the serum calcitonin level is higher than 40 pg/mL. The decision to perform a prophylactic central neck dissection is generally made on the basis of multiple factors such as patient age, pathogenic variant, presence of concomitant PHPT, and the vascularity of the parathyroid glands. Selective autotransplantation of parathyroid glands that were devascularized during a prophylactic thyroidectomy and/or central neck clearance is recommended. A selective approach also significantly reduces the detrimental outcome of hypoparathyroidism.
The MEN2B RET variant M918T is associated with approximately 100% incidence of MTC in the first years of life  and is considered the most aggressive MEN2 phenotype. In patients with MEN2A, the ATA-H high-risk codon 634 pathogenic variant is much more likely to be associated with invasive or metastatic MTC and development of persistent or recurrent disease than pathogenic variants in codons 804, 618, or 620. One series of 503 at-risk individuals with ATA-MOD category pathogenic variants (including codons 533, 609, 611, 618, 620, 791, and 804) reported cumulative penetrance rates, median time to MTC, and positive predictive value of preoperative calcitonin. The risk of developing MTC by age 50 years ranged from 18% to 95%, depending on the codon, with codon 620 having the highest penetrance. Most patients with MTC had node-negative disease, confirming the more indolent disease course that had been previously reported with these pathogenic variants. Although an elevated preoperative calcitonin level strongly predicted the presence of MTC, relatively high false-negative rates (low normal calcitonin levels with MTC) were noted for many of the codons. This information is useful when counseling carriers of pathogenic variants regarding the extent of surgical resection.
The ATA recommends compartment-directed lymph node dissection for local or regional disease (no evidence of distant metastases) in the following situations:
Although basal calcitonin levels may not be able to identify all patients with MTC preoperatively, this test has utility as a predictor of postoperative remission, lymph node metastases, and distant metastases. In one study of 224 patients from a single institution, preoperative basal calcitonin levels greater than 500 pg/mL predicted failure to achieve biochemical remission. The authors of this study found that nodal metastases started appearing at basal calcitonin levels of 40 pg/mL (normal, <10 pg/mL). In node-positive patients, distant metastases emerged at basal calcitonin levels of 150 pg/mL to 400 pg/mL. Another study of 308 RET pathogenic variant carriers found that a normal basal preoperative calcitonin excluded the presence of lymph node metastases (negative predictive value, 100%). Therefore, the preoperative basal calcitonin level is a useful prognostic indicator and may help guide the surgical approach.
With regard to prognosis, structural and metastatic disease recurrence is common in germline RET pathogenic variant carriers and can happen up to 20 years after initial treatment. Despite this, overall survival (OS) is generally favorable, with one study citing an OS rate of 92% at 10 years.
Patients who have had total thyroidectomy will require lifelong thyroid hormone replacement therapy. The dosing of medication is age-dependent and treatment may be initiated on the basis of ideal body weight. For healthy adults aged 60 years and younger with no cardiac disease, a reasonable starting dose is 1.6 µg/kg to 1.8 µg/kg given once daily. Older patients may require 20% to 30% less thyroid hormone. Children metabolize T4 more rapidly than adults and consequently require relatively higher replacement by body weight. Depending on the age of the child, replacement is typically between 2 µg/kg to 6 µg/kg. It is important to note, however, that replacement is preferred over suppressive therapy. Since C-cell tumors are not thyroid-stimulating hormone (TSH)–dependent for growth, the T4 therapy for patients with MTC therefore may be adjusted to maintain a TSH within the normal reference range. Thyroglobulin measurement may also be useful for adjusting and maintaining TSH levels within a normal reference range to prevent additional regrowth of remnant thyroid tissue.
Level of evidence (central neck dissection): 5
Level of evidence (hormone replacement therapy): 3c
Level of evidence (therapeutic thyroidectomy): 4
Chemotherapy and radiation therapy are not effective against MTC.[4,164,165] Targeted molecular therapies using multikinase inhibitors to block RET functions are being used to manage MTC. The use of vandetanib and cabozantinib is approved by the U.S. Food and Drug Administration for adult patients with progressive metastatic MTC who are ineligible for surgery. A phase III study found that progression-free survival (PFS) was longer in adults who received vandetanib than in those who received placebo. A phase I/phase II study of children with MEN2B found an objective partial response rate of 47% with vandetanib. Subsequent follow-up analysis of this cohort revealed that a partial response was seen in 10 of 17 patients; stable disease was seen in an additional 6 individuals. Median PFS was 6.7 years. A double-blind phase III trial that compared cabozantinib with placebo in 330 patients with progressive MTC showed an improvement in median PFS across all subgroups.[169,170] In this trial, patients who had pathogenic variants, including RET or RAS, were more likely to have a prolonged PFS compared with patients lacking both pathogenic variants. Prospective studies may further clarify whether particular pathogenic variants can be used to guide therapy. Neither cabozantinib nor vandetanib has demonstrated improved OS.[166,169,170] Importantly, these agents are not effective at inhibiting some MEN2 RET variants, specifically those at codon 804, making genotype an important consideration for treatment with RET inhibitors. Further, a 2018 study has demonstrated the development of resistance to these agents through somatic acquisition of a V804M mutation in RET. Finally, multikinase inhibitors are associated with significant toxicities, possibly due to their off-target effects on other kinases. Other multikinase inhibitors for targeting RET are being studied in clinical trials; however, they may only provide limited advantages over vandetanib and cabozantinib. For these reasons, ongoing studies are focusing on the development of selective RET inhibitors with fewer off-target effects that are able to block the activity of all RET variant forms and the use of combination therapy in MTC. Future studies will likely focus on the development of new targeted therapies and the use of combination therapy in MTC.[175,176] There are two U.S. Food and Drug Administration–approved RET inhibitors (pralsetinib and selpercatinib) that are now available for patients with MTC and differentiated thyroid cancers that have a RETtranslocation or point mutation.
Level of evidence (vandetanib): 2
Level of evidence (cabozantinib): 1
(Refer to the PDQ summary on Thyroid Cancer Treatment [Adult] for more information about the treatment of thyroid cancer.)
Treatment for MEN2-related PHEO
PHEO may be either unilateral or bilateral in patients with MEN2. Laparoscopic adrenalectomy (anterior or posterior) is the recommended approach after appropriate preoperative medical blockade for the treatment of unilateral PHEO.[1,90,98,177] The risks, benefits, and potential of life-threatening adrenal insufficiency should be considered at the time of the initial operative planning. If disease appears unilateral, the contralateral gland may develop metachronous disease in 17% to 72% of patients.[5,178] In one series, 23 patients with a unilateral PHEO and a macroscopically normal contralateral adrenal gland were treated initially with unilateral adrenalectomy. A PHEO developed within the retained gland in 12 (52%) of these patients, occurring a mean of 11.9 years after initial surgery. During follow-up, no patient experienced a hypertensive crisis or other problems attributable to an undiagnosed PHEO. In contrast, 10 of 43 patients (23%) treated with bilateral adrenalectomy experienced at least one episode of acute adrenal insufficiency. Thus, unilateral adrenalectomy appears to represent a reasonable management strategy for unilateral PHEO in patients with MEN2.[1,180,181] Many experts suggest consideration of a cortical-sparing technique, even at the initial operation for seemingly unilateral disease.[1,182] (Refer to the Interventions section in the Familial PHEO and Paraganglioma Syndrome section of this summary for more information.) Because of the risk of contralateral gland disease, periodic surveillance (serum or urinary catecholamine measurements) for the development of disease in the contralateral adrenal gland is recommended.
Regarding the operative approach, several studies examined the value of a posterior retroperitoneoscopic adrenalectomy and found it to be safe and effective, with very low mortality and a low rate of minor complications, and conversion to open surgery required rarely.[178,183,184,185,186,187,188,189]
Level of evidence: 4
Treatment for hyperparathyroidism
Most patients with MEN2-related parathyroid disease are either asymptomatic or diagnosed incidentally in the preoperative planning or at the time of thyroidectomy. Typically, the hypercalcemia (when present) is mild, although it may be associated with increased urinary excretion of calcium and nephrolithiasis. As a consequence, the indications for surgical intervention are generally similar to those recommended for patients with sporadic PHPT. In general, fewer than four of the parathyroid glands are involved at the time of detected abnormalities in calcium metabolism.
Treatment of hyperparathyroidism typically employs some extent of surgical removal of the involved glands. Cure of hyperparathyroidism was achieved surgically in 89% of one large series of patients; however, 22% of resected patients in this study developed postoperative hypoparathyroidism. Five patients (9%) had recurrent hyperparathyroidism. This series employed various surgical techniques, including total parathyroidectomy with autotransplantation to the nondominant forearm (4 of 11 patients [36%] developed postoperative hypoparathyroidism), subtotal parathyroidectomy (6 of 12 patients [50%] developed hypoparathyroidism), and resection only of glands that were macroscopically enlarged (3 of 29 patients [10%] developed hypoparathyroidism). These data indicate that excision of only those parathyroid glands that are enlarged appears to be sufficient therapy in most cases.
Some investigators have suggested using the MEN2 subtype to decide where to place the parathyroid glands that are identified at the time of thyroid surgery. For patients with MEN2B in whom the risk of parathyroid disease is quite low, the parathyroid glands may be left in situ in the neck. For adult patients with MEN2A, in whom the glands have been inadvertently devascularized during primary surgical treatment for MTC, it is suggested that the glands needing reimplantation be implanted in the nondominant forearm. This approach minimizes the need for further surgical intervention in the neck should hyperparathyroidism develop or recur.[1,157,190,191] For children, the risk/benefit ratio must be carefully weighed to avoid overtreatment and subsequent aparathyroidism. It is important to confirm that the remnant or autotransplanted parathyroid tissue is functional.[1,98,193,194]
Medical therapy of hyperparathyroidism has gained popularity with the advent of calcimimetics, agents that sensitize the calcium-sensing receptors on the parathyroid glands to circulating calcium levels and thereby reduce circulating PTH levels. In a randomized, double-blind, placebo-controlled trial, cinacalcet hydrochloride was shown to induce sustained reduction in circulating calcium and PTH levels in patients with PHPT. In patients who are high-risk surgical candidates, those with recurrent hyperparathyroidism, or those in whom life expectancy is limited, medical therapy may be a viable alternative to a surgical approach. Consequences of long-term therapy with cinacalcet are unknown.
Mode of inheritance
All of the MEN2 subtypes are inherited in an autosomal dominant manner. For the child of someone with MEN2, the risk of inheriting the MEN2 pathogenic variant is 50%. Some individuals with MEN2, however, carry a de novo pathogenic variant; that is, they carry a new pathogenic variant that was not present in previous generations of their family and thus do not have an affected parent. The proportion of individuals with MEN2 who have an affected parent varies by subtype.
MEN2A: About 95% of affected individuals have an affected parent. It is appropriate to evaluate the parents of an individual with MEN2A for manifestations of the disorder. In the 5% of cases that are not familial, either de novo pathogenic variants or incomplete penetrance of the mutant allele is possible.
FMTC: Multiple family members are affected; therefore, all affected individuals inherited the mutant gene from a parent.
MEN2B: About 50% of affected individuals have de novo RET gene pathogenic variants, and 50% have inherited the pathogenic variant from a parent.[197,198] The majority of de novo pathogenic variants are paternal in origin, but cases of maternal origin have been reported.
Siblings of a proband: The risk to siblings depends on the genetic status of the parent, which can be clarified by pedigree analysis and/or DNA-based testing. In situations of apparent de novo pathogenic variants, germline mosaicism in an apparently unaffected parent must be considered, even though such an occurrence has not yet been reported.
Attitudes toward preimplantation genetic testing
One study explored the attitudes of individuals with MEN1 and MEN2 toward preimplantation genetic testing (PGT). Ninety-one clinic-based patients from a single U.S. institution who had MEN1 and an MEN1 pathogenic variant or MEN2 and a RET pathogenic variant were surveyed. The study found that 30% (10 of 33) of those with MEN1 and 37% (21 of 57) of those with MEN2 were aware of PGT; 82% (27 of 33) of those with MEN1 and 61% (34 of 56) of those with MEN2 thought PGT should be offered; and 61% (19 of 31) of those with MEN1 and 43% (23 of 54) of those with MEN2 would consider PGT.
The psychosocial impact of genetic testing for pathogenic variants in RET has not been extensively studied. Published studies have had limitations such as small sample size and heterogeneous populations; thus, the clinical relevance of these findings should be interpreted with caution. Identification as the carrier of a pathogenic variant may affect self-esteem, family relationships, and quality of life. In addition, misconceptions about genetic disease may result in familial blame and guilt.[202,203] Several review articles outline both the medical and psychological issues, especially those related to the testing of children.[204,205,206,207] The medical value of early screening and risk-reducing treatment are contrasted with the loss of decision-making autonomy for the individual. Lack of agreement between parents about the value and timing of genetic testing and surgery may spur the development of emotional problems within the family.
One study examined levels of psychological distress in the interval between submitting a blood sample and receiving genetic test results. Those individuals who experienced the highest level of distress were younger than 25 years, single, and had a history of responding to distressful situations with anxiety. Pathogenic variant–positive parents whose children received negative test results did not seem to be reassured, questioned the reliability of the DNA test, and were eager to continue screening of their noncarrier children.
A small qualitative study (N = 21) evaluated how patients with MEN2A and family members conceptualized participation in lifelong high-risk surveillance. Ongoing surveillance was viewed as a reminder of a health threat. Acceptance and incorporation of lifelong surveillance into routine health care was essential for coping with the implications of this condition. Concern about genetic predisposition to cancer was peripheral to concerns about surveillance. Supportive interventions, such as Internet discussion forums, can serve as an ongoing means of addressing informational and support needs of patients with MTC undergoing lifelong surveillance.
Multiple endocrine neoplasia type 4 (MEN4) is a novel, rare syndrome with clinical features that overlap with the other MEN syndromes. The most common phenotype of the 19 established cases of MEN4 that have been described to date is primary hyperparathyroidism (PHPT), followed by pituitary adenomas. MEN4 is caused by germline pathogenic variants in the tumor suppressor gene CDKN1B (12p13.1). This syndrome was discovered initially in rats (MENX)  and later in humans (MEN4). The syndrome has the phenotype of being multiple endocrine neoplasia type 1 (MEN1)-like. The incidence of CDKN1B variants in patients with an MEN1-related phenotype is difficult to estimate, but it is likely to be in the range of 1.5% to 3.7%.[3,4,5]Pathogenic variants leading to the MEN4 phenotype are transmitted in an autosomal dominant fashion.
PHPT due to parathyroid neoplasia affects approximately 80% of the reported cases of MEN4. PHPT occurs at a later age in MEN4 than in MEN1 (mean age ~56 y vs. ~25 y, respectively), with a female predominance. There have been no reports of PHPT recurrence after surgical resection, which might indicate that PHPT in MEN4 represents an overall milder disease spectrum than in MEN1. Pituitary involvement in MEN4 is the second most common manifestation of the disease, affecting approximately 37% of the reported cases. Pituitary adenomas in MEN4 vary and include nonfunctional, somatotropinoma, prolactinoma, or corticotropinoma types. The age at diagnosis for these lesions also varies widely, from 30 years to 79 years. The youngest patient reported to have MEN4 presented at age 30 years with acromegaly. Pancreatic neuroendocrine tumors (NETs) have been rare, with only a few cases reported. These include duodenopancreatic or gastrointestinal NETs that could be nonfunctioning or hormonally active and may secrete several substances, including gastrin, insulin, adrenocorticotropic hormone, or vasoactive intestinal polypeptide. Although adrenal neoplasia is a frequent finding in MEN1, only one case of nonfunctional bilateral adrenal nodules has been reported in MEN4. Skin manifestations that are commonly reported in MEN1, such as lipomas, angiofibromas, and collagenomas, have not been reported in MEN4. There is no known genotype -phenotype correlation.
Genetics, Inheritance, and Genetic Testing
The CDKN1B variant codes for p27Kip1 (commonly referred to as p27 or KIP1), a putative tumor suppressor gene that regulates cell cycle progression. Alterations in this gene lead to a decrease in expression of p27 protein, triggering uncontrolled cell cycle progression. Although the loss of one allele of p27 is a frequent event in many human cancers, the remaining allele is rarely mutated or lost by loss of heterozygosity in human cancers.Somatic mutations or germline pathogenic variants in CDKN1B have also been identified in patients with sporadic PHPT, small intestinal NETs, lymphoma, and breast cancer. These findings demonstrate a novel role for CDKN1B as a tumor susceptibility gene in other neoplasms.[8,9,10]
To date, only 19 cases having CDKN1B germline variants have been reported in the medical literature. Thirteen pathogenic germline variants that have been frameshift, nonsense, or missense variants have been described.[11,12]
Index cases or individuals with MEN1-like features and negative results of MEN1 genetic testing are offered genetic counseling and testing for MEN4. Confirmation of an MEN4 diagnosis is only made with genetic testing for CDKN1B variants. In clinical practice, patients with asymptomatic or symptomatic PHPT who are also young (typically <30 y) and have multigland disease, parathyroid carcinoma, or atypical adenoma, or those with a family history or evidence of syndromic disease and negative for MEN1 or RET, are candidates for genetic testing for CDKN1B using accredited laboratories. For those with proven disease, screening is also offered to a first-degree relative with or without MEN1 features. The identification of a germline CDKN1B variant should prompt periodic clinical biochemical screening for MEN4.
Surveillance of CDKN1B pathogenic variant carriers should be performed, though guidelines have yet to be established.[8,13] Currently, surveillance is primarily clinical and concentrates on evidence of growth hormone excess, with annual biochemical evaluation for insulin-like growth factor-1 and annual blood work for PHPT. For known carriers, surveillance begins at adolescence. The role of imaging has not been established.
For parathyroid and pituitary disease, the treatment is surgical, in accordance with treatment for other familial syndromes. (Refer to the MEN1 section of this summary for more information.)
A study of 293 MEN1 pathogenic variant–positive cases and 30 MEN1 pathogenic variant–negative cases, all with the MEN1 phenotype, showed that the pathogenic variant–negative cohort developed disease manifestations later in life, with improved life expectancy. One of the limitations in applying this finding to MEN4 is that only 1 of these 30 MEN1-negative patients was CDKN1B positive.