Gastrin-releasing peptide (GRP) is a neuropeptide that acts through G protein-coupled receptors (GPCRs) involved in signal transmission in both central and peripheral nervous systems. Gastrin-releasing peptide (GRP) regulates numerous functions of the gastrointestinal and central nervous systems, including release of gastrointestinal hormones, smooth muscle cell contraction, and epithelial cell proliferation. It is a potent mitogen for neoplastic tissues. GRPR is aberrantly expressed in numerous cancers such as those of the lung, colon, and prostate.