GRP and cancer: Several neuropeptides such as vasoactive intestinal peptide (VIP), bombesin (Bom), gastrin releasing peptide (GRP), calcitonin (Calci), parathyroid hormone-related peptide (PTHRP) and endothelin (Endo), as well as a neurotransmitter serotonin (Sero) have been shown to increase the proliferative capacity of cancer cells.19, 20, 21 In addition, some of these neuropeptides can increase the invasion and migration of cancer cells leading to metastasis.22, 23, 24 Because of the extensive role in carcinogenesis, VIP has drawn a special focus.