PTHLH and Hypercalcemia: The pathophysiology through which hypercalcemia may occur in malignancy is via three mechanisms: 1) tumor secretion of parathyroid hormone-related protein (PTHrP), also known as humoral hypercalcemia of malignancy (HHM); 2) release of cytokines after metastases to bone tissue; and 3) tumor production of calcitriol.2