A humanized monoclonal antibody directed against parathyroid hormone-related protein (PTH-rP). As a poly-hormone with diverse biological roles, PTH-rP is expressed by normal tissues, acting in local tissue environments in a variety of ways; it is commonly overexpressed by breast, prostate, and other cancers, acting systemically by promoting bone resorption, inhibiting calcium excretion from the kidney, inducing hypercalcemia, and possibly playing a role in the formation of bony metastases. By blocking the effects of PTH-rP on calcium metabolism, monoclonal antibody CAL may inhibit cancer-related hypercalcemia.