Calcitonin testing and thyroid cancer: which statement is accurate?

• A. Calcitonin is produced by parafollicular C cells and elevated levels suggest medullary thyroid carcinoma; other cancers typically do not raise calcitonin.
• B. Calcitonin is produced by follicular cells and is a marker for medullary thyroid carcinoma.
• C. Calcitonin is produced by adipose tissue.
• D. Calcitonin levels are not useful in cancer.

Answer: (B)