GRPR (gastrin-releasing peptide receptor)

The gastrin-releasing peptide receptor (GRPR) is a G-protein-coupled receptor for bombesin and GRP whose expression is high in hormone-sensitive prostate cancer and falls with castration resistance. It is overexpressed in primary and hormone-naive prostate cancer, often in PSMA-negative tumours, as well as in ER-positive breast cancer and GIST, which makes it a complementary theranostic target to PSMA. Bombesin-like radioligands exploit it: 68Ga-RM2 PET for imaging and 177Lu-NeoB (Novartis) for therapy are in clinical trials. Because expression declines as disease becomes castration-resistant, GRPR agents may suit earlier disease or PSMA-negative patients rather than replacing PSMA therapy. A newcomer can think of GRPR as a second radioactive address on prostate cancer, useful where PSMA is dim.