PTH and cancer: Hypercalcemia associated with cancer may be caused by: (i) systemic secretion of parathyroid hormone-related protein (PTHrP), a peptide produced by tumors with close homology in the N-terminal sequence to parathyroid hormone (PTH); (ii) osteolytic metastases, or, more rarely, by (iii) ectopic production of 1,25-dihydroxyvitamin D, which leads to intestinal hyperabsorption of calcium and increased osteoclastic bone reabsorption, and (iv) ectopic hyperparathyroidism [9].