Impact of antibiotic use on response to treatment with immune checkpoint inhibitors.

143Background: There is an emerging evidence that the gut microbiome may influence anti-tumor immune response during treatment with checkpoint inhibitors (CPIs). A number of factors can cause gut microbiome dysbiosis including the use of antibiotics (ABX). We hypothesized that the use of ABX during immunotherapy can adversely affect the efficacy of CPIs. We explored the prevalence of ABX use amongst patients (pts) using CPIs, and whether the use of ABX influences the response to CPIs. Methods: We performed an institutional retrospective review of all the pts treated with CPIs from 2/2015-3/2018. A patient was considered to have used ABX if he or she was prescribed ABX within 6 months before or after, initiating CPIs. Statistical analysis was done using logistic regression with overall response rate (ORR) (CR, PR and SD) as the outcome. 9 separate analyses were done: one for each temporality (30 days, 60 days, 6 months) and use-order (before, after, neither) combination. Odds ratios for ORR as univariate a...