GRPR and lung cancer: After obtaining encouraging results with GnRH-III-based PDCs directed towards the gonadotropin-releasing hormone receptor (GnRH-R) [15,16,17,18], our research group has focused on the gastrin-releasing peptide receptor (GRP-R, or bombesin receptor 2, BB2), which is overexpressed in several malignancies, such as prostate, breast and lung cancer, while being poorly expressed physiologically in healthy tissues [8,19,20,21].