A 45-year-old woman has a firm 2 cm left thyroid nodule with cervical lymphadenopathy. FNA shows sheets of spindle-shaped cells with amyloid stroma on Congo red staining. Serum calcium is normal. Which tumour marker confirms the diagnosis?
- A Thyroglobulin
- B Calcitonin ✓
- C Carcinoembryonic antigen
- D Parathyroid hormone-related protein
Correct answer: B. Calcitonin
Explanation
Amyloid stroma from calcitonin prohormone deposition plus spindle-shaped C cells defines medullary thyroid carcinoma, which secretes calcitonin; a markedly elevated basal level confirms the diagnosis. Thyroglobulin is the marker for differentiated papillary and follicular cancers and is not produced by C cells. Carcinoembryonic antigen may be elevated in advanced medullary cancer but is neither specific nor confirmatory. Calcium is characteristically normal because calcitonin has little effect on adult calcium homeostasis.
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.