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
[{'content': 'The commonest cause of raised serum calcium is - \nSelect and explain. \nA. Ectopic secretion, B. Parathyroid hyperplasia, C. Parathyroid adenoma, D. Parathyroid carcinoma', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Primary hyperparathyroidism is the most common cause of hypercalcemia overall.\nThe frequency of the various parathyroid lesions underlying the hyperfunction is as follows : -\n\nParathyroid adenoma - 75% to 80%\nPrimary hyperplasia - 10% to 15%\n\u200bParathyroid carcinoma- < 5%\n\nAfter hyperparathyroidism, malignancy is the 2nd most common cause of hypercalcemia by one of the following mechanisms.\n\nOsteolysis\nSecretion of parathormone related peptide.', 'role': 'assistant'}]