Parathyroid hormone-related protein and skin cancer

Parathyroid hormone-related protein (PTHrP) is now well established as the major, if not the sole mediator of the humoral hypercalcaemia of malignancy. This is the phenomenon of elevated blood calcium in the absence of bony metastases in patients with certain solid tumours, most commonly squamous cell carcinoma (SCC) of the lung, but also occurring in SCC at other sites including skin, and other cancers including melanoma. Although discovered because of its hormonal action in cancer, there is at present no indication that PTHrP acts as a circulating hormone in normal animals or in humans after birth, with the possible exception of the period during lactation. Along with its significant effects on calcium metabolism in cancer patients, PTHrP is widely expressed in mammalian tissue, and evidence to date indicates that the major physiological role of PTHrP is as a paracrine factor affecting growth and development of cells in several tissues.