Improved Efficacy To Cytotoxic Agents Chemotherapy After Immune Checkpoint Inhibitors Exposure In Metastatic Gastric Cancer

297 Background: An association between improved responses to chemotherapy after exposure to vaccine-based immunotherapy has been previously reported in other cancers. However, it is unclear whether the chemotherapy response improves after exposure to immunotherapy, such as immune checkpoint inhibitors (ICIs). The objective of this retrospective study was to evaluate whether chemotherapy (4th-line) would yield improved efficacy when given after exposure to anti-PD-1 antibody in metastatic gastric cancer (mGC). Methods: We investigated retrospectively clinical characteristics at baseline of mGC patients who received chemotherapy after progression of anti-PD-1 antibody (Nivolumab) between February 2018 and July 2019. Anti-PD-1 antibody was adapted as third-line therapy. Inclusion criteria for the analysis reported herein: histologically proven adenocarcinoma; ECOG PS 0-2; adequate organ functions; and received chemotherapy including 5-fluoropyrimidines (5-FU), platinum, and taxane or irinotecan. We evaluated efficacy outcomes, including ORR, DCR by RECIST version 1.1, PFS, and OS. Results: Out of 27 treated with anti-PD-1 antibody, 10 patients were evaluable for responses and eligible to be included in this analysis. Patient characteristics were as follows: median age (range), 72 (50-88) years; male/female, 8/2; ECOG PS (0/1/2), 4/5/1; HER2 (+/-), 5/5; histology (differentiated/undifferentiated), 5/5; metastatic lesions (LN/peritoneum/liver/lung), 5/3/1/3; number of metastatic sites (1/≥2), 5/5; number of prior CTx regimens (3/4/5), 10/0/0; median period (range) from first line CTx, 18.8 (7.9-47.1) months; and CTx regimens (CPT-11/PTX/S-1+Oxaliplatin), 7/2/1; Among the 10 patients, 1 achieved a partial response, giving an ORR of 10.0%. Six patients had stable disease and three had progressive disease. The DCR was 70%. Median PFS and OS were 5.5M and 8.5M, respectively. These were no new irAEs appeared during CTx. Conclusions: In mGC patients, our study demonstrated that increased efficacy to cytotoxic agents chemotherapy given after exposure to ICI was higher as compared to our historical data from the pre-anti-PD1 era. Updated results will be presented.