Bombesin is a 14-aa peptide originally isolated from the fire-bellied toad. It has two mammalian homologs, neuromedin and Gastrin-Releasing Peptide (GRP). It binds with high affinity to the GRP receptor, a member of the G-protein-coupled receptor family. It stimulates gastrin release from G cells, and acts in the brain to stop eating behavior. Bombesin is also a tumor marker for lung small cell carcinoma, neuroblastoma, pancreatic cancer and gastric cancer.