GRPR and glioblastoma: Bombesin (Bom) is a 14-amino-acid linear peptide, primarily obtained from frog skin, which specifically interacts with the gastrin-releasing peptide receptor (GRPR), a seven-transmembrane receptor expressed more abundantly on the membranes of tumor cells in lung, colon, breast, and brain (glioblastoma) cancers than normal tissues [124,128].