<prompt> The commonest cause of raised serum calcium is -Ectopic secretionParathyroid hyperplasiaParathyroid adenomaParathyroid carcinoma  <response>: Primary hyperparathyroidism is the most common cause of hypercalcemia overall.The frequency of the various parathyroid lesions underlying the hyperfunction is as follows : -Parathyroid adenoma - 75 to 80Primary hyperplasia - 10 to 15Parathyroid carcinoma- 5After hyperparathyroidism, malignancy is the 2nd most common cause of hypercalcemia by one of the following mechanisms.OsteolysisSecretion of parathormone related peptide. 