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MTC is generally the first manifestation of MEN 2A.
Probands with MTC typically present with a neck mass or neck pain, usually before age 35 years.
Pheochromocytomas are identified in 50% of individuals with multiple endocrine neoplasia type 2A and multiple endocrine neoplasia type 2B.
Furthermore, those with multiple endocrine neoplasia type 2A have a 20–30% risk for primary hyperparathyroidism.
The FMTC subtype comprises approximately 10–20% of cases of MEN 2.
By operational definition, MTC is the only clinical manifestation of FMTC.
Approximately 75% of affected individuals have a Marfanoid habitus, often with kyphoscoliosis or lordosis, joint laxity, and decreased subcutaneous fat.
MTC is diagnosed histologically when nests of C cells appear to extend beyond the basement membrane and to infiltrate and destroy thyroid follicles.
Immunohistochemistry for calcitonin expression may be performed as a pathologic diagnostic adjunct.
Multiple endocrine neoplasia type 2 is historically composed of three clinical subtypes, all of which are associated with germline mutations in the RET proto-oncogene.
Multiple endocrine neoplasia type 2A, familial medullary thyroid carcinoma, and multiple endocrine neoplasia type 2B are collectively associated with a 70–100% risk of medullary thyroid carcinoma by age 70 years.
Individuals with multiple endocrine neoplasia type 2B often have distinct physical features including mucosal neuromas of the lips and tongue, medullated corneal nerve fibers, ganglioneuromatosis of the gastrointestinal tract, distinctive facies with enlarged lips, and a “Marfanoid” body habitus.