Abstract 1969: Distinctive profiles on immunotherapy responders versus non responders in Chilean gastric cancer patients

Abstract Background: Gastric cancer (GC) is the leading cause of cancer death in Chile, claiming >3,000 lives per year. On April 2021, the US Food and Drug Administration approved the combined use of Nivolumab (immunotherapy) plus chemotherapy as frontline treatment for advanced GC. Unfortunately, as occurs with any therapy, a proportion of treated patients are either unresponsive or display poor responses. Our study sought to obtain a profile of GC patients categorized as responders or non-responders to immunotherapy in order to identify better predictors of response and novel targets for treatment refractory patients. Methods: A total of 50 GC patients were included into our study. Demographic and basic information was obtained from medical records. Additionally, we retrieved information on response to treatment, histological type, PDL1 and HER2 status. Nucleic acid samples were collected from a subset of 45 patients (responders and non-responders) and analyzed by massive analysis of cDNA ends (MACE-seq) assessing 3’ mRNA sequencing. Results: Patients were predominantly male (76%) and advanced stage (III/IV; 98%). Within this subset, 26 were responders and 24 were non-responders. Among clinical variables, body mass index was significantly higher on responders versus non-responders (p=0.026). Among responders, tumors were predominantly located on the gastro-esophagic junction. As expected, responders also displayed a higher prevalence of HER2- and PDL1+. Our 3’ MACE analysis confirmed distinct profiles on responders compared to non-responders. Conclusions: Our findings confirm distinctive profiles among Chilean GC patients categorized as responders or non-responders to immunotherapy. These results could deliver novel markers that may serve as predictors of response to immunotherapy (as an alternative to PDL1) or to identify patients more likely to be refractory to treatment. Future studies should further confirm and validate these findings in a larger sample. Citation Format: Mauricio P. Pinto, Matias Muñoz Medel, Miguel Córdova Delgado, Ignacio N. Retamal, Patricio Manque, Alejandro Berkovits, Maria Paz Rodriguez, Juvenal A. Rios, Benjamin Garcia-Bloj, Gareth Owen, Marcelo Garrido. Distinctive profiles on immunotherapy responders versus non responders in Chilean gastric cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1969.