GRP and small cell lung carcinoma: Gastrin and cholecystokinin are expressed also in lung, ovaries, thyroid, and brain.[17,18] Bombesin stimulates the growth of human breast cancer cells in vitro[19] and it is a powerful growth factor in the small cell lung cancer.[20] In addition, NETs produce other growth factors like platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), transforming growth factor (TGF).[21] A possible therapeutic strategy might be blocking receptors for these neuropeptides.