Hypercalemia of Malignancy is defined as a pathological rise in blood calcium in response to a malignant tumor. Hypercalcemia of Malignancy is a common paraneoplastic syndrome which is encountered with great frequency in small animal medicine. Neoplastic cells are responsible for producing humoral factors which result in increased ionized calcium concentrations in the blood. The increase in ionized calcium concentrations cause many adverse clinical signs observed in patients suffering with neoplastic disease. Homeostasis of calcium in the body is maintained in a narrow range due to its importance in intracellular and extracellular processes. Regulation of calcium is mediated mainly in the interactions of parathyroid hormone (PTH) and vitamin D metabolites (calcitriol). The minute to minute control of calcium homeostasis in the blood is controlled by PTH and the day to day control of calcium homeostasis is mediated by the influence of calcitriol. PTH is responsible for raising ionized blood calcium levels in the normal animal.