This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Calcitonin is a marker of ? 
Select and explain. 
A. Prostate cancer, B. Medullary carcinoma of thyroid, C. Pheochromocytoma, D. Pancreatic cancer
B: Medullary carcinoma of thyroid
Answer: B: Medullary carcinoma of thyroid 
Explanation: Ans. is 'b' i.e., Medullary carcinoma of thyroid