Which marker is most appropriate to monitor for recurrence of medullary thyroid carcinoma?

• A. α-Fetoprotein
• B. Norepinephrine
• C. Human chorionic gonadotropin
• D. Calcitonin

Answer: (D)

Medullary thyroid carcinoma comes from parafollicular (C) cells, which secrete calcitonin. Because the tumor itself produces calcitonin, its serum level directly reflects tumor burden. After treatment, calcitonin should fall toward normal; if levels stay elevated or rise over time, or show a rising trend (doubling time), this signals residual disease or recurrence. That makes calcitonin the most appropriate marker to monitor for recurrence.

The other markers don’t fit this cancer biology: α-fetoprotein is linked to hepatocellular carcinoma and some germ cell tumors; norepinephrine is a marker for pheochromocytoma and other neuroendocrine processes; human chorionic gonadotropin is associated with germ cell tumors. While useful in other contexts, they don’t track medullary thyroid carcinoma recurrence.