Clinical manifestations and diagnosis of multiple endocrine neoplasia type 2

INTRODUCTION — Multiple endocrine neoplasia type 2 (MEN2) is an autosomal dominant disorder with an estimated prevalence of 1 per 30,000 in the general population. MEN2 is subclassified into two distinct syndromes: types 2A (MEN2A) and 2B (MEN2B). Within MEN2A, there are four variants: classical MEN2A, MEN2A with cutaneous lichen amyloidosis (CLA), MEN2A with Hirschsprung disease (HD), and familial medullary thyroid cancer (FMTC) (table 1) [1].

The genetic defect in these disorders involves the RET proto-oncogene on chromosome 10. MEN2A and 2B are inherited in an autosomal dominant pattern with very high penetrance. In both syndromes, there is an occurrence of multicentric tumor formation in all organs where the RET proto-oncogene is expressed. The thyroid, parathyroid, and adrenal glands are at risk for developing tumors that may reduce life expectancy and quality of life. The excellent prognosis for medullary thyroid cancer (MTC) diagnosed at its earliest stage underscores the importance of early diagnosis for sporadic and hereditary MTC [2].

This topic will review the clinical manifestations, diagnosis, and evaluation of MEN2. The genetics and treatment of this disorder are discussed separately. Sporadic MTC is also discussed separately.

●(See "Classification and genetics of multiple endocrine neoplasia type 2".)

●(See "Approach to therapy in multiple endocrine neoplasia type 2".)

●(See "Medullary thyroid cancer: Clinical manifestations, diagnosis, and staging".)

●(See "Medullary thyroid cancer: Surgical treatment and prognosis".)

CLINICAL FEATURES — Multiple endocrine neoplasia type 2 (MEN2) is subclassified into two distinct syndromes: types 2A (MEN2A) and 2B (MEN2B) (table 1) [3-6].

MEN2A is characterized by medullary thyroid cancer (MTC), pheochromocytoma, and primary parathyroid hyperplasia (see 'MEN2A' below). MEN2B is characterized by MTC and pheochromocytoma but not hyperparathyroidism. It is associated with additional clinical features (eg, mucosal neuromas) not seen in MEN2A. (See 'MEN2B' below.)

MEN2A — Within multiple endocrine neoplasia type 2A (MEN2A), there are four variants (table 1) [1] (see "Classification and genetics of multiple endocrine neoplasia type 2"):

●Classical MEN2A

●MEN2A with cutaneous lichen amyloidosis (CLA)

●MEN2A with Hirschsprung disease (HD)

●Familial MTC (FMTC)

The clinical manifestations of MEN2A depend upon which organs are involved, which in turn is dependent upon the specific RET mutation. While the penetrance of MTC is nearly 100 percent, there is much inter- and intrafamily variability in the other manifestations of MEN2A.

FMTC is a variant of MEN2A in which there is a strong predisposition to MTC but not the other clinical manifestations of MEN2A (or MEN2B).

Medullary thyroid cancer — MTC is a neuroendocrine tumor of the parafollicular or C cells of the thyroid gland. Most cases of MTC (75 percent) are sporadic, but as many as 25 percent of all MTCs are familial (table 2) [7]. MTCs in patients with MEN2 are multicentric and concentrated in the upper third of the thyroid gland, reflecting the normal distribution of parafollicular cells (picture 1).

Among patients with MEN2, virtually all patients develop clinically apparent MTC, often early in life [1]. In MEN2A-associated MTC, the peak incidence of index cases is in the third decade of life, and it is usually earlier in MEN2B. Specific RET mutations are associated with characteristic age-specific penetrance of MTC (table 3), as well as characteristic prevalence of the extrathyroidal manifestations. The age of onset of MTC is decreasing over time for many mutations, likely related to earlier surgical intervention. As an example, the earliest age of onset described for mutations in codons 634 and 918 is 10 months and 2 months, respectively [8].

If diagnosed as an index case, the clinical presentation and manifestations of MEN2-associated MTC are similar to those of sporadic MTC, except that sporadic MTC typically presents later in life. The most common presentation is that of a solitary thyroid nodule or cervical lymphadenopathy. Fine-needle aspiration (FNA) biopsy shows eccentrically placed nuclei that are larger and more pleomorphic than those of normal follicular cells. The cytoplasm may be slightly granular and is usually configured as a tear drop or cytoplasmic tail. If the diagnosis is suspected, immunocytologic staining for calcitonin should be performed. (See "Medullary thyroid cancer: Clinical manifestations, diagnosis, and staging", section on 'Diagnosis'.)

Less common presentations specific to MEN2-associated MTC include recognition during a search initiated after an associated disease (such as pheochromocytoma or hyperparathyroidism) becomes apparent, diarrhea caused by gastrointestinal secretion of fluid and electrolytes, and flushing due to the secretion of other peptides by the tumor. In rare cases, MTC causes Cushing syndrome due to ectopic production of corticotropin (ACTH). (See "Causes and pathophysiology of Cushing syndrome".)

In asymptomatic patients identified through calcitonin or DNA testing, initiated due to the presence of an associated disease or to a family history of MEN2, MTC is often diagnosed in its preneoplastic state, C-cell hyperplasia. Basal serum calcitonin concentrations usually correlate with tumor mass and are almost always high in patients with a palpable tumor. In patients with small tumors and those with C-cell hyperplasia, the values may be normal but rise excessively after calcium or pentagastrin infusion [9]. (See 'Biochemical testing' below.)

The presence of C-cell hyperplasia is defined based upon microscopy criteria: the presence of an increased number of diffusely scattered C cells (≥7 per thyroid follicle), complete follicles surrounded by C cells, or distribution of C cells beyond the normal anatomical location [1,10]. C-cell hyperplasia can occur in a reactive (secondary) form or a neoplastic form (precursor to MTC in MEN2). Neoplastic C-cell hyperplasia is diagnosed when nests of C cells appear to extend beyond the basement membrane and to infiltrate and destroy thyroid follicles (picture 2) [11]. Reactive C-cell hyperplasia is considered to be caused by a stimulus from outside the C cell and probably is not premalignant (picture 3). Hyperparathyroidism, chronic renal insufficiency, chronic lymphocytic thyroiditis, and follicular thyroid tumors have been associated with reactive C-cell hyperplasia [12].

Pheochromocytoma — Pheochromocytoma occurs in approximately 50 percent of patients with MEN2. The frequency of pheochromocytoma depends upon the specific underlying RET mutation [1,13]. Some RET mutations are associated with a higher penetrance of pheochromocytoma. As an example, in one study, the penetrance of pheochromocytoma was 25 percent by age 30 years, 52 percent by age 50 years, and 88 percent by age 77 years in patients with RET codon 634 mutations [14].

As with MTC, pheochromocytomas in MEN2 occur earlier than sporadic forms. Although they may develop as early as 8 to 12 years of age, the mean age of presentation is 25 to 32 years, depending on the RET mutation [15-17]. It is unusual for pheochromocytoma to precede the development of MTC and be the initial manifestation of MEN2. In patients who have undergone regular screening, pheochromocytomas have usually become evident approximately 10 years later than C-cell hyperplasia or MTC [18]. Thus, pheochromocytomas in MEN2 are usually identified during screening or through heightened vigilance for symptoms in patients with known or suspected MEN2.

Rarely, pheochromocytoma may be the first manifestation of MEN2 [19,20]. In such patients, symptoms are similar to those in patients with sporadic pheochromocytomas and may include attacks (paroxysms) of anxiety, headache, diaphoresis, palpitations, or tachycardia. However, in one report, only approximately one-third had hypertension at the time of diagnosis [21]. The severity of symptoms may depend upon the specific RET mutation [22]. The diagnosis of pheochromocytoma includes biochemical testing and, once a diagnosis of pheochromocytoma is established, imaging studies. The clinical manifestations and diagnosis of pheochromocytoma are reviewed in detail separately. (See "Clinical presentation and diagnosis of pheochromocytoma".)

Sporadic pheochromocytomas are almost always unilateral [23,24]. In contrast, pheochromocytomas in MEN2 have been reported to be bilateral in approximately 30 to 100 percent of patients [15,21,24]. Thus, once the diagnosis of pheochromocytoma in MEN2 is established, the possibility of bilateral disease must be carefully evaluated. Extraadrenal pheochromocytoma is rare in MEN2 but does occur, especially in accessory adrenal glands (picture 4 and picture 5) or in extraadrenal chromaffin cells (paragangliomas) [25,26]. (See "Paragangliomas: Epidemiology, clinical presentation, diagnosis, and histology", section on 'MEN2'.)

In most studies, the percentage of MEN2A-associated pheochromocytomas that are malignant is considerably less than the 10 percent rate of malignancy reported for sporadic pheochromocytomas [7,25]. (See "Clinical presentation and diagnosis of pheochromocytoma".)

Other heritable syndromes associated with pheochromocytoma include von Hippel-Lindau (VHL) syndrome, neurofibromatosis type 1, and paraganglioma syndromes. This topic is reviewed in more detail elsewhere. (See "Pheochromocytoma in genetic disorders".)

Primary hyperparathyroidism — Primary hyperparathyroidism in MEN2A is almost always multiglandular. It has been reported in 10 to 25 percent of patients with MEN2A, depending upon the specific RET mutation [1,7,27,28]. The hyperparathyroidism in MEN2A is often mild and asymptomatic. In patients who have undergone regular screening, the diagnosis is established by finding high (or inappropriately normal) serum parathyroid hormone (PTH) concentrations in the presence of hypercalcemia. (See "Primary hyperparathyroidism: Diagnosis, differential diagnosis, and evaluation".)

The recurrence rate after apparently successful subtotal parathyroidectomy is less than that in multiple endocrine neoplasia type 1 (MEN1) [29,30] and is similar to the excellent long-term results seen in patients with nonfamilial primary hyperparathyroidism.

There has been a suggestion that parathyroid disease in MEN2A may somehow be a consequence of the C-cell abnormalities, based upon a low reported incidence of parathyroid disease in patients in whom C-cell hyperplasia was detected early and treated by total thyroidectomy [31,32]. In one report, as an example, none of 22 patients who underwent thyroidectomy developed hyperparathyroidism after more than 10 years of follow-up [31]. Why this might occur and whether the risk is indeed lower after thyroidectomy is not clear. It seems unlikely that hypercalcitoninemia per se is the stimulus for the parathyroid tumors for the following reasons:

●Hyperparathyroidism is not associated with MEN2B, FMTC, or sporadic MTC, all of which can be characterized by sustained hypercalcitoninemia.

●The RET gene is expressed in MEN2A-associated parathyroid tumors [33].

●A particular RET mutation, Cys to Arg at codon 634, may be preferentially found in MEN2 families that have hyperparathyroidism [3,34].

●Primary hyperparathyroidism rarely may be the first manifestation of MEN2 [35].

These data imply that the initial stimulus to parathyroid cell proliferation in MEN2A, while often mild, is probably related to expression of the mutant RET protein within parathyroid tissue. It is interesting in this context, although not of direct clinical importance, that calcium suppression testing in normocalcemic patients has suggested that mild abnormalities in parathyroid function may be common in MEN2A [36].

Other associated diseases

Cutaneous lichen amyloidosis — CLA, also termed lichen planus amyloidosis (LPA), is a rare skin condition and can occur both sporadically and as a familial disease. The hereditary forms are transmitted in an autosomal dominant fashion, and an association between CLA and MEN2A has been established in some families [37].

The skin lesion is usually described as pruritic, scaly, papular, pigmented, and located in the interscapular region or on the extensor surfaces of the extremities (picture 6A-B) [36]. Amyloid deposition has been documented histologically [38,39]. Keratin-like peptides have been found in the amyloid deposits but not calcitonin-like peptides [37]. CLA is thought to result from a primary neuropathy [39-41]. This is an attractive hypothesis with respect to CLA being a rare manifestation of MEN2A since RET is expressed in the peripheral and central nervous system [42-44].

Several different RET codon 634 mutations have been described in MEN2A/CLA families [45,46], and both dermal and nondermal manifestations segregate with the mutation [45]. These same RET mutations are also found in MEN2A families without evidence of CLA, suggesting the influence of "modifying genes" or other factors cooperating with the RET mutation in the expression of the CLA phenotype. CLA was also reported in a patient with a RET codon 804 mutation [47]. CLA kindreds without MEN2A have not had demonstrable germline RET mutations [46].

Hirschsprung disease — HD is characterized by the absence of autonomic ganglion cells within the distal colonic parasympathetic plexus, resulting in chronic obstruction and megacolon. (See "Congenital aganglionic megacolon (Hirschsprung disease)".)

HD is a heterogenic disorder, occurring both in a familial and in a sporadic form. In approximately 50 percent of familial and 15 to 35 percent of sporadic HD patients, mutations in the RET gene are involved. In one study, HD was found in 50 percent of children in families with a C620 mutation [48]. Most HD cases arise from loss-of-function mutations, RET haploinsufficiency, RET polymorphisms, or haplotypes of the RET promoter region. RET proto-oncogene testing in infants presenting with HD is useful and may identify new MEN2A kindreds [49,50]. (See "Classification and genetics of multiple endocrine neoplasia type 2", section on 'Germline mutations causing Hirschsprung disease'.)

MEN2B — Multiple endocrine neoplasia type 2B (MEN2B) is an autosomal dominant disorder characterized by MTC and pheochromocytoma but not hyperparathyroidism. MTC occurs in almost all patients. The tumor develops at an earlier age and is more aggressive than in MEN2A [7]. Surgery is often not curative. In one large study, death from MTC occurred in 50 percent of patients with MEN2B versus 9.7 percent of those with MEN2A [51]. Thus, early diagnosis and prevention are crucial. Thyroidectomy as early as the neonatal period may be indicated in patients with MEN2B identified by genetic screening. (See "Approach to therapy in multiple endocrine neoplasia type 2", section on 'Timing of surgery'.)

Pheochromocytoma occurs in approximately 50 percent of patients with MEN2B [1,52]. Pheochromocytomas in MEN2B occur earlier than sporadic forms. However, it is unusual for pheochromocytoma to precede the development of MTC and be the initial manifestation of MEN2.

The syndrome of MEN2B also includes mucosal neuromas, typically involving the lips and tongue, and intestinal ganglioneuromas. Patients with MEN2B also have development abnormalities, a decreased upper/lower body ratio, skeletal deformations (kyphoscoliosis or lordosis), joint laxity, Marfanoid habitus, and myelinated corneal nerves. Disturbances of colonic function are common, including chronic constipation and megacolon [52]. Unlike patients with Marfan syndrome, MEN2B patients do not have ectopia lentis or aortic abnormalities [7].

DIAGNOSIS — Multiple endocrine neoplasia type 2 (MEN2) should be suspected in any patient with medullary thyroid cancer (MTC) or pheochromocytoma, particularly when the tumors occur at a young age (<35 years), are multicentric, or when more than one family member is affected. The diagnosis of MEN2 is based upon the presence of the classical clinical features, family history, and genetic testing.

MEN2 — In an index patient with one or two of the classical clinical features, identification of a germline RET mutation or the identification of the clinical features of multiple endocrine neoplasia type 2 (MEN2) in other first-degree relatives is required to make the diagnosis of MEN2 [27].

In the absence of an autosomal dominant familial inheritance pattern or RET mutation, at least two of the classical clinical features of MEN type 2A (MEN2A; MTC, pheochromocytoma, primary hyperparathyroidism) are required to make a clinical diagnosis of MEN2A.

In the absence of an autosomal dominant familial inheritance pattern or RET mutation, the majority of classical clinical features of MEN type 2B (MEN2B; MTC, pheochromocytoma, mucosal neuromas, Marfanoid habitus, intestinal ganglioneuromas, myelinated corneal nerves) are required to make a clinical diagnosis of MEN2B [27].

Although a patient with the classical clinical features of MEN2 and similar clinical features in one or more first-degree relatives does not need RET mutation analysis for diagnosis, genetic testing (where available) is performed in all patients with clinical MEN2 in order to identify the specific RET mutation and facilitate family screening (table 4). There are rare families, however, with clinical features of MEN2A in the absence of an identifiable RET mutation. (See 'Screening of family members in MEN2 kindreds' below.)

●Genetic testing – For the index patient with suspected MEN2A, all exons should be sequenced, starting with the most commonly mutated codons in exons 10 and 11 and then, if negative, sequentially proceeding to exons 8, 13, 14, 15, and 16 [1]. If no germline mutation is found, only a small risk of hereditary MTC remains. In this case, sequencing the entire RET coding region is an option to identify a RET mutation.

For the index patient with the MEN2B phenotype, initial testing should be for the RET codon M918T mutation in exon 16 and, if negative, for the A883F mutation in exon 15. If no mutations are identified, the entire RET coding region should be sequenced [1].

Once a germline RET mutation is identified in an index case, RET mutation analysis should also be performed in first- and second-degree family members. The screening of family members is discussed below. (See 'Screening of family members in MEN2 kindreds' below.)

Occasionally, older patients with MTC, a negative family history, and no clinical features of MEN2 may nonetheless harbor a cryptic germline RET mutation. Evaluation of patients with apparently sporadic MTC should include genetic testing for germline RET mutations as germline RET gene mutations are detected in approximately 4 to 6 percent of apparently sporadic cases [53]. The indications for genetic testing for the detection of unsuspected heritable MEN2 in patients with apparently sporadic MTC or pheochromocytoma (eg, unilateral disease, a negative family history, and no other signs or symptoms of MEN2) is reviewed separately. (See "Medullary thyroid cancer: Clinical manifestations, diagnosis, and staging", section on 'Genetic screening in sporadic MTC' and "Pheochromocytoma in genetic disorders", section on 'Genetic screening'.)

Familial medullary thyroid cancer variant — The familial MTC (FMTC) variant of MEN2A is characterized by the presence of a RET germline mutation in families or an individual with MTC who do not develop pheochromocytoma or primary hyperparathyroidism [1].

EVALUATION

RET mutation analysis — For patients diagnosed with multiple endocrine neoplasia type 2 (MEN2) based upon the classical clinical features and family history (typically medullary thyroid cancer [MTC] and a family member with MTC), evaluation should include RET mutation analysis (if not already performed) in order to identify the specific RET mutation to facilitate family screening (table 4). (See 'Diagnosis' above and "Medullary thyroid cancer: Clinical manifestations, diagnosis, and staging", section on 'Genetic screening in sporadic MTC' and 'Genetic screening' below.)

If a family member is positive for the RET mutation, prophylactic thyroidectomy is indicated. The timing of thyroidectomy is based upon the specific RET mutation and, in some cases, serum calcitonin levels. (See "Approach to therapy in multiple endocrine neoplasia type 2", section on 'Preventive surgery'.)

Screening for MEN2-associated tumors — Patients with multiple endocrine neoplasia type 2 (MEN2; and their affected family members) also require screening for MEN2-associated tumors. In all patients diagnosed with MEN2, we measure plasma fractionated metanephrines (as the initial screen for pheochromocytoma) and serum calcium (to rule out hyperparathyroidism requiring concomitant surgical intervention). For patients with MEN2 who present with pheochromocytoma rather than MTC, we measure serum calcitonin and obtain a thyroid and neck ultrasound to assess for the presence of MTC.

Screening for MEN2-associated tumors in families of the index patient is reviewed below. (See 'Monitoring for MEN2-associated tumors' below.)

Pheochromocytoma — Screening for pheochromocytoma is mandatory in all patients with inherited MTC syndromes. If pheochromocytoma is found, it should be removed prior to thyroidectomy.

For the index patient with MTC, we measure plasma fractionated metanephrines as the initial screen for pheochromocytoma. If biochemical results are positive, adrenal imaging with computed tomography (CT) or magnetic resonance imaging (MRI) is the next step. (See "Clinical presentation and diagnosis of pheochromocytoma", section on 'Additional evaluation after biochemical diagnosis'.)

If the initial screening tests for pheochromocytoma are negative, it is important to evaluate for pheochromocytoma yearly (table 5). Details of biochemical screening to detect pheochromocytomas, including in MEN2 patients, is reviewed elsewhere. (See "Clinical presentation and diagnosis of pheochromocytoma", section on 'High risk for pheochromocytoma'.)

Hyperparathyroidism — When the diagnosis of MEN type 2A (MEN2A)-related MTC is established, we measure serum calcium to rule out hyperparathyroidism requiring concomitant surgical intervention. Hyperparathyroidism is not part of the MEN type 2B (MEN2B) syndrome, and therefore, patients with MEN2B do not require evaluation for hyperparathyroidism.

If the serum calcium is elevated, we measure intact parathyroid hormone (PTH). The diagnosis is established by finding high (or inappropriately normal) serum PTH concentrations in the presence of hypercalcemia. (See "Primary hyperparathyroidism: Diagnosis, differential diagnosis, and evaluation".)

If the serum calcium is normal, we measure serum calcium yearly to detect the development of hyperparathyroidism (table 5).

Medullary thyroid cancer — Most index patients with MEN2 present with MTC and, therefore, do not require monitoring for its development. For patients with MEN2 who present with pheochromocytoma, we measure serum calcitonin and obtain a thyroid and neck ultrasound to assess for the presence of MTC. If there is no evidence of MTC, we continue to screen annually (table 6).

Additional evaluation of patients who have been diagnosed with MEN2-related MTC is similar to that in sporadic MTC and should include measurement of serum calcitonin, carcinoembryonic antigen (CEA), and ultrasonography of the neck (if not already performed). (See "Medullary thyroid cancer: Clinical manifestations, diagnosis, and staging", section on 'Evaluation'.)

SCREENING OF FAMILY MEMBERS IN MEN2 KINDREDS — Once a germline RET mutation is identified in an index case, RET mutation analysis should be performed in first- and second-degree family members. Affected family members also require screening for multiple endocrine neoplasia type 2 (MEN2)-associated tumors. (See 'Genetic screening' below and 'Monitoring for MEN2-associated tumors' below.)

Advances in the molecular genetics underlying the MEN2 syndromes have resulted in DNA testing becoming the optimal test for their detection. The role of RET DNA testing in MEN2 kindreds is better established than testing for MEN1 mutations in multiple endocrine neoplasia type 1 (MEN1) families. This is because identification of specific RET mutations predicts particular phenotypes (age of onset, aggressiveness of medullary thyroid cancer [MTC], and presence or absence of other endocrine neoplasms) and, thus, guides surveillance and management (table 3 and table 5 and table 6) [2].

In the past, pentagastrin and calcium stimulation tests were used to stimulate calcitonin secretion by thyroid C cells and assess for the diagnosis of MTC in family members. However, RET mutation screening is available for MEN2, and therefore, these tests have lost their clinical significance with respect to diagnosis of MEN2 [54]. Genetic testing in known MEN2 families has several clinically important advantages over the pentagastrin or calcium tests:

●It provides clinical benefit that should accrue from earlier surgery for known MEN2 gene carriers as the genotype correlates with the age at initial diagnosis of MTC (table 3).

●It definitively establishes that an individual does not carry the MEN2 mutation and eliminates the need for biochemical testing.

●It avoids unnecessary thyroidectomy in genetically normal subjects in MEN2 families. It is now clear, from retrospective DNA testing, that such subjects can have falsely positive pentagastrin tests [55,56].

However, biochemical tests are still used in families who meet the clinical criteria for MEN2 but have negative sequencing of the entire RET coding region or for families who refuse genetic testing. (See 'When RET mutation is unknown' below.)

Genetic screening — In general, the primary and most compelling purpose of genetic screening in human tumor predisposition syndromes is to prevent disease-related morbidity and mortality that would otherwise occur [2,27,57,58]. Genetic counseling and genetic testing for RET germline mutations should be offered to the following groups [1]:

●First-degree relatives of a patient with proven germline RET mutation

●Parents whose infants or young children have the clinical characteristics of MEN type 2B (MEN2B)

●Patients with cutaneous lichen amyloidosis (CLA)

●Families whose infants or young children have Hirschsprung disease (HD)

In an MEN2 family, a sample from one subject already known to be affected should be tested in order to determine the specific RET mutation for that family. All subjects of unknown status in that family should then be definitively genotyped. RET genotyping requires only a small blood sample and can therefore be performed at birth or soon thereafter. At the latest, genotyping should be done before the time at which prophylactic thyroidectomy would be performed in the event of a positive result.

●Known RET mutation present – For those with RET mutations, prophylactic thyroidectomy in family members is timed based upon the specific DNA mutation in the RET proto-oncogene occurring in the family (table 6). The risk-benefit equation is strengthened by the ease of thyroid hormone replacement after thyroidectomy and the relatively low morbidity of the surgery, even in children, when performed by high-volume surgeons [59]. The timing of prophylactic thyroidectomy is reviewed separately. (See "Approach to therapy in multiple endocrine neoplasia type 2", section on 'Preventive surgery'.)

●Known RET mutation absent – A family member who has not inherited the specific RET mutation that causes that family's MTC needs no further evaluation.

Thus far, family screening efforts appear to be suboptimal, as a high proportion of patients continue to receive less than optimal initial surgical treatment. According to the population-based Surveillance, Epidemiology, and End Results (SEER) registry, there has been no change in stage at diagnosis [60]. However, the proportion of patients undergoing total thyroidectomy increased, and disease-specific survival improved. Although the SEER registry does not contain information regarding hereditary or biochemical results, an estimated 50 percent had a familial form of MTC (FMTC). Summary information concerning MEN2 may be useful for counseling patients and affected families. Family alliances can provide such information: Genetic Testing Registry (GTR) or EndocrineWeb.

Sensitivity/specificity — One potential problem relates to the rare MEN2 families with no detectable RET mutation. In addition, as with any genetic test, other potential sources of error exist such as sample mix-up, cross-contamination of the polymerase chain reactions used in the tests, and DNA polymorphisms that would prevent amplification of one RET allele, a situation that could result in a false-negative screening test. To date, however, neither false-negative nor false-positive RET tests have been described in MEN2 families in which a specific RET mutation was detected in an index case.

Availability of genetic diagnosis — Genetic diagnosis of MEN type 2A (MEN2A), FMTC, and MEN2B is readily available commercially. A list of testing laboratories is available at the MD Anderson Cancer Center website and through the genetic testing resource Genetic Testing Registry (GTR). In Europe, a listing of commercial laboratories can be found at the European Directory of DNA Diagnostic Laboratories.

Clinicians should inquire as to the protocol and methodology of the offered RET DNA test. One important issue is whether all relevant exons (exons 10, 11, and 16, and, if those are negative, exons 8, 13, 14, and 15) will be sequenced if the RET mutation in that family is unknown.

Counseling — Before blood samples are taken for DNA analysis, detailed information about the consequences of DNA analysis must be provided to the family. Psychological support may well be needed before DNA test results are disclosed and during follow-up after diagnosis to minimize distress. Written consent must be obtained [61]. Given the rarity of this disease and the potential complications of a total thyroidectomy in young children, patients should be referred to academic centers with expertise in MEN2.

Reproductive options — Patients with MEN2 and a known familial RET mutation should be counseled that prenatal testing and preimplantation genetic testing (PGT) are available options if they choose to pursue fertility [1]. Prenatal testing is performed in the first or second trimester via chorionic villus sampling or amniocentesis, respectively. PGT is done as part of in vitro fertilization (IVF); single embryonic cells are tested for the RET mutation. Only embryos without a RET mutation are then transferred to the uterus. The various reproductive options available to prospective parents require thoughtful discussion and genetic counseling.

Monitoring for MEN2-associated tumors — Affected family members require screening for multiple endocrine neoplasia type 2 (MEN2)-associated tumors.

When RET mutation is known — When the RET mutation is known, monitoring for MEN2-associated tumors is based upon the specific mutation and degree of risk it confers for MTC, pheochromocytoma, and primary hyperparathyroidism.

Medullary thyroid cancer — Children with certain RET mutations can develop clinically apparent MTC at an early age. The goal in patients with known RET mutations (but without clinically apparent disease) is to perform a prophylactic thyroidectomy before MTC develops or when it is still confined to the thyroid gland (table 6). (See "Approach to therapy in multiple endocrine neoplasia type 2", section on 'Preventive surgery'.)

Children with the highest risk mutation (codon 918) should have thyroidectomy within the first year of life and, therefore, do not require monitoring prior to thyroidectomy.

For children with high-risk mutations (codons 634, 883), we begin monitoring at age three years, and for children with moderate risk mutations, we begin monitoring at age five years. We monitor with an annual physical examination, neck ultrasound, and measurement of serum calcitonin. The detection of a serum calcitonin level (basal or stimulated) above the upper limit of normal is an indication for surgery.

Pheochromocytoma — The risk of developing pheochromocytoma is variable depending upon genotype [62-64]. For children in the highest and high-risk categories, screening for pheochromocytoma should begin by age 11 years (table 5). For children in the moderate-risk category, we begin screening by age 16 years. Patients should be screened yearly by measuring plasma fractionated metanephrines or 24-hour urinary metanephrines and normetanephrines. If biochemical results are positive, adrenal imaging with computed tomography (CT) or magnetic resonance imaging (MRI) is the next step. (See "Clinical presentation and diagnosis of pheochromocytoma", section on 'Additional evaluation after biochemical diagnosis'.)

There is large variability in the penetrance of pheochromocytoma among different reported kindreds, depending upon the specific RET germline mutation. These findings help guide screening and therapy for MEN2 patients [65-69]. As an example, compared with families with mutations in codons 634 and 918, pheochromocytomas are rare in families with mutations in codons 533, 609, 611, 618, 620, 630, 633, 666, 768, 790, 791, 804, and 891, although they do still occur.

Due to screening programs, pheochromocytomas may be diagnosed at a young age and before symptoms are present.

Hyperparathyroidism — The hyperparathyroidism in MEN2A is often mild and asymptomatic. In one study, the mean age at diagnosis was 33 years, but children diagnosed as young as two years of age has been reported [1,28,70,71]. Biochemical screening for hyperparathyroidism should be performed yearly beginning at age 11 years in high-risk patients and 16 years in moderate-risk patients (patients in the highest risk category [MEN2B] are not at risk for developing hyperparathyroidism) (table 5) [1]. We measure serum calcium (corrected for albumin). If it is elevated, we measure intact parathyroid hormone (PTH). The diagnosis is established by finding high (or inappropriately normal) serum PTH concentrations in the presence of hypercalcemia. (See "Primary hyperparathyroidism: Diagnosis, differential diagnosis, and evaluation".)

When RET mutation is unknown

Biochemical testing — For closely related MEN2 family members who refuse DNA analysis for themselves or their children, or for families who meet the clinical criteria for MEN2 but have negative sequencing of the entire RET coding region, biochemical testing can be performed to detect MEN2-related tumors. If biochemical testing is used, yearly testing starting at age five and continuing until at least age 35 years (or until a positive test occurs) is necessary [7]. For families with a clinical diagnosis of MTC prior to age five years, biochemical screening for MTC should begin at the youngest age of first diagnosis.

●Pheochromocytoma and primary hyperparathyroidism – To screen for pheochromocytoma, obtain plasma fractionated metanephrines or 24-hour urinary metanephrines and normetanephrines. To screen for primary hyperparathyroidism, obtain serum calcium. (See "Clinical presentation and diagnosis of pheochromocytoma", section on 'Initial biochemical tests' and "Primary hyperparathyroidism: Diagnosis, differential diagnosis, and evaluation", section on 'Diagnosis'.)

●MTC – Either a pentagastrin or a calcium stimulation test can be used to screen for C-cell hyperplasia/MTC. Where available (not in the United States), pentagastrin is the preferred stimulation test. Given the availability of serum calcitonin assays with improved functional sensitivity, some experts believe that provocative testing is no longer necessary, whereas others consider it useful for identifying C-cell hyperplasia and for determining the timing of thyroidectomy in mutation carriers [1,72,73].

Owing to the unavailability of pentagastrin in many countries, there is growing interest in the calcium stimulation test. However, there are few data using the calcium stimulation as a confirmatory test in patients with elevated basal calcitonin levels, and cutpoints for the discrimination of normal, C-cell hyperplasia, and medullary thyroid cancer (MTC) have not been standardized [74]. In one study, basal and stimulated calcitonin levels were measured in over 100 patients with thyroid disease (MTC in remission or persistence, RET gene mutation carriers, nodular goiter) and in 16 healthy volunteers [75]. In all groups, the levels of calcitonin stimulated by either pentagastrin or calcium were significantly correlated. In this study, calcium stimulated calcitonin levels above 32.6 pg/mL (females) and 192 pg/mL (males) had the best accuracy to differentiate normal subjects from patients with C-cell hyperplasia or MTC [75]. Criteria for abnormal calcitonin values may vary in local or commercial laboratories [72].

•Pentagastrin stimulation test – The pentagastrin stimulation test uses a slow intravenous injection of pentagastrin (0.5 mcg/kg body weight) over three minutes. Blood samples for calcitonin are obtained at baseline and two and five minutes after pentagastrin infusion [76,77]. If stimulated calcitonin values are ≥200 pg/mL, MTC is likely and thyroidectomy and lymphadenectomy are required. If values are <100 pg/mL, the risk of MTC is low and periodic monitoring of basal and stimulated serum calcitonin levels is recommended. If the stimulated calcitonin values are between 100 and 200 pg/mL, the risk is uncertain. Such values could be indicative of C-cell hyperplasia or micro MTC. Some advise surgery [78,79], while others observation (following calcitonin levels) [80].

Side effects of pentagastrin include abdominal cramping, extremity paresthesia, and feeling of warmth, lasting up to one to two minutes [77]. Pentagastrin is not available in many countries, including the United States.

•Calcium stimulation test – The calcium stimulation test uses an infusion of calcium gluconate (2.5 mg elemental calcium/kg body weight over 30 seconds) administered in a fasting state (no food after midnight) [55,77]. Blood samples for calcitonin are obtained at baseline and two and five minutes after the stimulus. In one study, calcium-stimulated calcitonin levels above 32.6 pg/mL (females) and 192 pg/mL (males) had the best accuracy to differentiate normal subjects from patients with C-cell hyperplasia or MTC [75].

The most common side effects are temporary flushing and feeling of warmth (98 percent) [77]. Facial paresthesias are less common (20 percent).

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Medullary thyroid cancer".)

SUMMARY AND RECOMMENDATIONS

●Classification – Multiple endocrine neoplasia type 2 (MEN2) is subclassified into two distinct syndromes: types 2A (MEN2A) and 2B (MEN2B) (table 1). Within MEN2A, there are four variants. The genetic defect in MEN2 involves the RET proto-oncogene on chromosome 10. MEN2A and 2B are inherited in an autosomal dominant pattern with very high penetrance. (See 'Introduction' above.)

●Clinical features

•MEN2A – MEN2A is characterized by medullary thyroid cancer (MTC), pheochromocytoma, and primary parathyroid hyperplasia. While the lifetime penetrance of MTC is nearly 100 percent, there is much inter- and intrafamily variability in MTC onset and in the other manifestations of MEN2A. (See 'Clinical features' above.)

•MEN2B – MEN2B is characterized by MTC and pheochromocytoma but not hyperparathyroidism. MTC occurs in almost all patients. The tumor develops at an earlier age and is more aggressive than in MEN2A; as a result, early diagnosis and prevention are crucial. The syndrome also includes mucosal neuromas, typically involving the lips and tongue, intestinal ganglioneuromas, and a Marfanoid habitus. Disturbances of colonic function are common, including chronic constipation and megacolon. (See 'Clinical features' above.)

●Diagnosis

•When to suspect – MEN2 should be suspected in any patient with MTC or pheochromocytoma, particularly when the tumors occur at a young age (<35 years), are multicentric, or when more than one family member is affected. (See 'Diagnosis' above.)

•Clinical criteria – The diagnosis of MEN2 is based upon the presence of the classical clinical features, family history, and genetic testing. In an index patient with one or two of the classical clinical features, identification of a germline RET mutation or the identification of the clinical features of MEN2 in other first-degree relatives is required to make the diagnosis of MEN2. (See 'MEN2' above.)

-MEN2A – In the absence of an autosomal dominant inheritance pattern or RET mutation, at least two of the classical clinical features of MEN2A (MTC, pheochromocytoma, primary hyperparathyroidism) are required to make the diagnosis.

-MEN2B – In the absence of an autosomal dominant familial inheritance pattern or RET mutation, the majority of classical clinical features of MEN2B are required to make a clinical diagnosis of MEN2B.

●Familial MTC – Familial MTC (FMTC) is characterized by the presence of a RET germline mutation in families or an individual with MTC who do not develop pheochromocytoma or primary hyperparathyroidism. Distinguishing the FMTC variant from classical MEN2A may be difficult in small families, and therefore, rigorous criteria for FMTC should be used in order not to miss a pheochromocytoma. (See 'Familial medullary thyroid cancer variant' above.)

●Evaluation

•RET mutation analysis – For patients diagnosed with MEN2 based upon the classical clinical features and family history (typically MTC and a family member with MTC), evaluation should include RET mutation analysis (if not already performed) in order to identify the specific RET mutation to facilitate family screening (table 4). (See 'RET mutation analysis' above.)

•Screening for MEN2-associated tumors – Patients with MEN2 also require screening for MEN2-associated tumors. In all patients diagnosed with MEN2-related MTC, we measure plasma fractionated metanephrines (as the initial screen for pheochromocytoma in patients with MEN2A or 2B) and serum calcium (to rule out hyperparathyroidism requiring concomitant surgical intervention in patients with MEN2A). For patients with MEN2 who present with pheochromocytoma rather than MTC, we measure serum calcitonin and obtain a neck ultrasound to assess for the presence of MTC. (See 'Screening for MEN2-associated tumors' above.)

If pheochromocytoma is found, it should be removed prior to thyroidectomy. If the initial testing for coexisting tumors is negative, it is important to evaluate the index patient for pheochromocytoma (MEN2A and 2B) and hyperparathyroidism (MEN2A) yearly (table 5).

●Screening of family members – Once a germline RET mutation is identified in an index case, RET mutation analysis should also be performed in first- and second-degree family members. Affected family members require screening for MEN2-associated tumors. (See 'Genetic screening' above and 'Monitoring for MEN2-associated tumors' above.)

Early diagnosis by screening of "at-risk" family members in MEN2 kindreds is important because identification of specific RET mutations predicts particular phenotypes (age of onset, aggressiveness of MTC, and presence or absence of other endocrine neoplasms) and, thus, guides surveillance for MEN2-associated tumors and management (table 3 and table 5 and table 6). (See 'Screening of family members in MEN2 kindreds' above and "Approach to therapy in multiple endocrine neoplasia type 2", section on 'Timing of surgery'.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Cornelis J Lips, MD, PhD, who contributed to earlier versions of this topic review.