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: Surgery
A biopsy from a mass shows parafollicular cells.
What is the tumor marker? 
Select and explain. 
A. Calcitonin, B. T4, C. Thyroxine, D. Thyroglobulin
A: Calcitonin
Answer: A: Calcitonin 
Explanation: Caclitonin is the tumor marker for MTC which arises from parafollicular cells.