Abstract Gastrin releasing peptide (GRP) is a 27 amino acid peptide which is present in many lung cancer cell lines (Moody et al., Science 1981; 214: 1246). High expression of the GRP receptor (R) is associated with advanced non-small cell lung cancer (NSCLC) (Mattei et al., Arch Pathol Lab Med 2014; 138: 98). GRP stimulates but the GRPR antagonist PD176252 inhibits the proliferation of NSCLC cells (Moody et al., Eur J Pharmacol 2003; 474: 21). Here the effects of GRP on the transactivation of the EGFR and HER2 were investigated in NSCLC cells. Six of 8 NSCLC tested had GRP-R mRNA whereas all the NSCLC cells had EGFR and HER2 mRNA. Addition of GRP to NCI-H1299 cells elevated cytosolic Ca2+, increased tyrosine phosphorylation of the ERK, EGFR and HER2 and increased colony number. The effects of GRP were blocked by PD176252. The transactivation of the EGFR and HER2 was inhibited by gefitinib (EGFR tyrosine kinase inhibitor (TKI)), lapatinib (EGFR and HER2 TKI), GM6001 (matrix metalloprotease inhibitor), PP2 (Src inhibitor), N-acetylcysteine (anti-oxidant) and transforming growth factor TGF) α antibody. By ELISA, GRP increased secretion of TGFα from lung cancer cells. PD176252, gefitinib, lapatinib and trastuzumab inhibited NSCLC growth. Activation of the GRPR in NSCLC cells may facilitate the formation of EGFR homodimers and EGFR/HER2 heterodimers. Citation Format: Terry W. Moody, Irene Ramos Alvarez, Robert T. Jensen. Gastrin-releasing peptide causes transactivation of the EGFR and HER2 in non-small cell lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1793.