A 40-year-old woman undergoes thyroidectomy for a solitary nodule. Histology shows nests of neuroendocrine cells with stromal deposits of amorphous eosinophilic material that stains with Congo red. Immunohistochemistry for the precursor protein of this amyloid would be positive for:

• A Serum amyloid A
• B Thyroglobulin
• C Transthyretin
• D Calcitonin (procalcitonin) ✓

Explanation

Medullary thyroid carcinoma, arising from parafollicular C cells, characteristically produces stromal amyloid derived from procalcitonin, the hormone secreted by these cells. Recognition of this tumor-associated amyloid is a useful diagnostic clue on histology. Thyroglobulin marks follicular-derived tumors such as papillary and follicular carcinoma, which do not form amyloid. Transthyretin and serum amyloid D define ATTR and AA amyloid types respectively, neither associated with medullary carcinoma.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.