This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thyroid Tumor, Subject name: Pathology
[{'content': 'Amyloid depostion and raised serum calcitonin levels are seen in which thyroid tumor? \nSelect and explain. \nA. Papillary carcinoma, B. Follicular carcinoma, C. Medullary carcinoma, D. Anaplastic carcinoma', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Acellular amyloid deposits derived from calcitonin polypeptides are present in stroma in many cases of medullary thyroid carcinoma. Calcitonin is readily demonstrable within cytoplasm of tumor cells & stromal amyloid by immunohistochemical methods. In addition to circulating calcitonin, secretion of carcinoembryonic antigen by neoplastic cells is useful biomarker, especially for presurgical assessment of tumor load & in calcitonin-negative tumors.', 'role': 'assistant'}]