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: Medicine
[{'content': 'Screening method for medullary carcinoma thyroid is : \nSelect and explain. \nA. Serum calcitonin, B. S. calcium, C. S. alkaline phosphate, D. S. acid phosphatase', 'role': 'user'}, {'content': "Answer: A \nExplanation: Answer is A (Serum Calcitonin): Medullary Carcinoma Thyroid are tumors of para-follicular 'C' cells derived from the neural crest, & are not derived from the cells of thyroid follicles. Since these pars follicular 'C' cells secrete CalcitoninQ, high level of serum Calcitonin (> 0.08 zsg/m1) are found. These levels fall after resection, & will rise again if the tumor recurs, making it the ideal candidate for screening tests. Also note :These cancers are associated with HypocalcemiaQ because calcitonin counteracts parathormnone.", 'role': 'assistant'}]