1196. Influence of antibiotic use on the effectiveness and safety of immune checkpoint inhibitors in Japan

BACKGROUND: It has been reported that antibiotic use changes the gut microbiome and alters the outcome of treatment with immune checkpoint inhibitors (ICIs). However, in Asia, this has not been well studied, and there is insufficient evidence to support these reports. METHODS: In this study, we investigated the concurrent use of antibiotics and the administration of PD-1 inhibitors in Japanese patients, and examined the relationship between antibiotics and the clinical benefit or safety of PD-1 inhibitors. RESULTS: In total, 152 patients were analyzed: 62 patients received systemic antibiotics within 2 months before or 1 month after the first dose of PD-1 inhibitors (the antibiotic group); the remaining patients comprised the non-antibiotic group. There was a significantly higher proportion of patients under 65 years of age in the antibiotic group. Overall survival (OS) was not reached in the antibiotic and non-antibiotic groups, and there was no statistically significant difference between the two groups (HR = 1.48) (Figure 1). Progression-free survival (PFS) was 3.29 months in the antibiotic group and was significantly shorter than that in the non-antibiotic group (5.99 months, HR = 1.75) (Figure 2). Multivariate analysis by Cox regression analysis also showed that PFS was shorter in the antibiotic group (HR=1.63). As age may be a confounding factor, we performed a stratified analysis, a common method used to adjust for bias. The results of the stratified log-rank test after adjustment for age showed that the PFS was significantly shorter in the antibiotic group. There were no statistically significant differences between the two groups in the response rate, incidence of adverse events of Grade 3 or above, and laboratory data (Table 1). Figure 1 [Image: see text] Figure 2 [Image: see text] Table 1 [Image: see text] CONCLUSION: Our results suggest that the use of antibiotics may affect the anticancer treatment outcomes of Japanese patients who are administered PD-1. DISCLOSURES: All Authors: No reported disclosures