A 38-year-old woman has elevated serum calcitonin and a thyroid nodule. Biopsy reveals nests and trabeculae of polygonal cells embedded in an amyloid-rich stroma that stains positively with Congo red. This tumor most commonly arises from which cell type?

• A Parafollicular C cells ✓
• B Follicular epithelial cells
• C Hurthle cells
• D Lymphoid cells

Explanation

Medullary thyroid carcinoma (MTC) arises from parafollicular C cells, which are of neural crest origin and secrete calcitonin. The amyloid in the stroma is composed of altered calcitonin precursor peptides. Elevated serum calcitonin is the key tumor marker. Approximately 25% of MTCs are familial and associated with RET proto-oncogene mutations, including MEN 2A and MEN 2B syndromes.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.