PURPOSE: Immune checkpoint inhibitor (ICI) therapy has become a mainstay in cancer treatment and even has first-line indications for malignancies such as melanoma, non-small cell lung cancer, and many others. Recent data has demonstrated that patients who received either antimicrobial therapy prior to or within the first 60 days of ICI initiation tend to have worse outcomes as measured by time to progression and overall survival. It has been theorized that this may be caused by the influence of the antibiotics on the intestinal microbiota. This study evaluates the effect of antimicrobial therapy on outcomes in veteran patients initiated on ICI therapy.
METHODS: A retrospective chart review was conducted on all patients initiated on ICIs from 1/1/2015 through 12/31/2017. Patients were evaluated as to whether they received any antibiotics within 30 days of ICI initiation or 60 days after ICI initiation or if they received no antibiotics during this time. Data was gathered using the Veterans Health Administration electronic health record. Primary endpoints evaluated were progression free survival (PFS) and overall survival (OS), using Wilcoxon signed-rank test. Descriptive statistics were utilized for patient demographics and antibiotic characteristic comparisons.
RESULTS: A total of 55 patients were identified as having been initiated on an ICI. Twenty-two patients (40%) had received antibiotic treatment prior to or concurrently with their ICI therapy and 33 patients (60%) did not. Median overall survival was numerically longer in patients who did not receive antibiotics at 10 months (95% confidence interval [CI], 4-17 mo.) versus 4 months in patients who received antibiotics (95% CI, 2-9 mo.). However, no significant benefit was observed in median PFS among patients who did not receive antibiotics compared to those who received antibiotics (5 mo. versus 11 mo.).
CONCLUSIONS: No association was observed between antibiotic use and ICI patient outcomes. Although this correlation has been suggested by several recent publications, the cause is not fully understood. This study has several limitations, which could explain why this association was not reproduced. Future investigation and monitoring will be helpful to elucidate any true relationship between ICI and antimicrobial therapies.