Recently, a protein with PTH-like activity, referred to as PTHrP (PTH-related protein), was isolated from a cancer cell line that was established from lung cancer tissue from a hypercalcaemic patient, and the structure of PTHrP mRNA was identified.
PTHrP is secreted by many squamous cell carcinomas, binds to the PTH receptor, and shares all of the known effects of PTH, on its target organs. Its normal physiological role is unknown but may be related to maternal-foetal calcium fluxes during pregnancy.
Since biological activities of PTHrP explain most of the clinical and laboratory finding of HM patients, and several clinical studies on a large number of HM patients have clarified that PTHrP substantially contributes to the development of HM, PTHrP is now the primary candidate for the factor responsible for HM.
