GRP and lung cancer: Cholecystokinin (CCK), gastrin, Gastrin releasing peptide (GRP), Neuromedin-B (NMB), bradykinin and vasopressin are considered growth-stimulatory neuropeptides as they act as autocrine/paracrine growth factors [19, 20] to promote cellular proliferation [21] in lung cancer and other cancers, whereas somatostatin is classified as a growth-inhibitory neuropeptide.