Multiple endocrine neoplasia type 2A (MEN2A) is caused by germline gain-of-function mutations in the RET proto-oncogene and includes medullary thyroid carcinoma (MTC), pheochromocytoma, and primary hyperparathyroidism. MTC arises from which thyroid cell type?
- A Parafollicular C cells secreting calcitonin ✓
- B Follicular cells secreting thyroid hormone
- C Sustentacular cells of the thyroid stroma
- D Hurthle cell (oxyphilic) variant of follicular cells
Correct answer: A. Parafollicular C cells secreting calcitonin
Explanation
Medullary thyroid carcinoma arises from parafollicular C cells, which are neural crest-derived neuroendocrine cells that secrete calcitonin. Elevated serum calcitonin is the diagnostic tumor marker. Histologically, MTC shows amyloid stroma (calcitonin-derived AA amyloid) and stains positive for calcitonin and CEA. In MEN2A, RET Cys634 mutations are most frequent; in MEN2B, RET Met918Thr predominates.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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