An extracellular calcium-sensing receptor (CaR) has been cloned from both bovine and human parathyroids, as well as from human kidney tissue and rat brain (Pollak, et al., Cell 75:1297-1303 (1993); Aida, et al.,Biochem. Biophys. Res. Commun. 214:524-529 (1995); Ruat, et al., Proc. Nat'l Acad. Sci. USA 92:3161-3165 (1995)). This receptor appears to play a key role in regulating extracellular calcium homeostasis (Pollak, et al., Nature Genet. 8:303-307 (1994); Pollak, et al., J. Clin. Invest. 93:1108-1112 (1994)).
Previous studies have suggested that calcium may be important in processes leading to tumor formation and spread. For example, it is known that cancerous breast and brain tissue tends to form microcalcifications (Galkin, et al. Radiology 124:245-249 (1977)) and calcium has been shown to stimulate cellular division and differentiation. Defining the relationship between calcium and tumor cell biology may lead to new clinical approaches to treating cancer patients. The present invention is based upon the discovery that CaR, a primary regulator of calcium, is expressed at abnormal levels in human tumors. This has led to the development of new diagnostic and therapeutic methods.