Purpose: Antibiotic exposure before immune checkpoint inhibitor (ICI) treatment can negatively affect outcomes through alteration in the gut microbiome, but large-scale evaluations are lacking. We performed a population-level retrospective cohort study to evaluate the impact of antibiotic exposure before starting ICI on overall survival (OS).
Patient and methods: Patients with cancer, age 65 years or older, who initiated treatment with ICIs between June 2012 and October 2018 in Ontario, Canada, were identified using systemic therapy administration data. The cohort was deterministically linked to other health care databases to obtain covariates and antibiotic prescription claim data at both 1 year and 60 days before ICI therapy. Multivariable Cox models evaluated the association between exposure and OS.
Results: Among the 2,737 patients with cancer who received ICIs, 59% and 19% of patients received antibiotics 1 year and 60 days before ICI therapy, respectively. Median OS was 306 days. Any antibiotic exposure within 1 year before ICI was associated with worse OS (adjusted hazard ratio [aHR], 1.12; 95% CI, 1.12 to 1.23; P = .03). In antibiotic class analysis, exposure to fluoroquinolones within 1 year (aHR, 1.26; 95% CI, 1.13 to 1.40; P < .001) or 60 days before ICI (aHR, 1.20; 95% CI, 0.99 to 1.45; P = .06) was associated with worse OS, with a dose effect seen on the basis of total weeks of exposure over 1 year (aHR, 1.07 per week; 95% CI, 1.03 to 1.11; P < .001) and 60 days (aHR, 1.12 per week; 95% CI, 1.03 to 1.23; P = .01).
Conclusion: In this population-level study, exposure to antibiotics and specifically fluoroquinolones before ICI therapy was observed to be associated with worse OS among older adults with cancer. Interventions aimed at altering the gut microbiome to boost immunogenicity may help improve outcomes for patients receiving ICIs with prior antibiotic exposure.