PTH Related Protein (PTHrP) is a peptide that acts as an endocrine, autocrine, paracrine, and intracrine hormone. It regulates endochondral bone development by maintaining the endochondral growth plate at a constant width. It also regulates epithelial-mesenchymal interactions during the formation of the mammary glands. It is secreted by most if not all tissues in the body and the active site of this peptide is structurally related to that of parathyroid hormone and it has similar effects in bone and kidney tissue, inducing hypocalcemia, hypophosphoremia and increased nephrogenic cyclic AMP. This test is done to determine whether high blood calcium levels are caused by an increase in PTH-related protein. PTH-related protein is produced by some cancers, including those of the lung, breast, head, neck, bladder, and ovaries, as well as leukemia and lymphoma. HIGH levels of PTH-related protein are the cause of high calcium levels in about two-thirds of cancer patients. This condition is called humoral hypercalcemia of malignancy (HHM).