This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Parathyroids, Subject name: Pathology
[{'content': 'A biopsy from a mass in the neck region revels the presence of parafollicular cells. Which of the following is the best marker for the follow up of this patient? \nSelect and explain. \nA. Calcitonin, B. Thyroglobulin, C. T4, D. T3', 'role': 'user'}, {'content': "Answer: A \nExplanation: Medullary Ca Arises from parafollicular cells or 'C' cells Associated with secretion of calcitonin. Associated with amyloid deposition. Standard marker is Calcitonin. In calcitonin negative medullary thyroid Ca - Tumor marker is carcinoembryonic Ag Familial medullary thyroid carcinomas In MEN-2 Associated with germline RET mutations-Constitutive activation of the receptor. RET mutations are also in nonfamilial (sporadic) medullary thyroid cancers.", 'role': 'assistant'}]