Antibiotic exposure within six months before systemic therapy was associated with lower cancer survival

Objectives: The objective of the study was to quantify associations between cancer survival and antibiotic exposure before systemic anticancer therapy. Study Design and Setting: This population-based cohort study compares cause-specific survival according to antibiotic exposure before non–immune checkpoint inhibitor (ICI) systemic therapy in patients diagnosed with single primary cancers in New South Wales between 2013 and 2016. Proportional hazards regression was used to control for confounding, with no antibiotic exposure in the six months before non-ICI systemic therapy serving as the comparator. Results: After adjusting for tumour spread, cancer site, age, sex and comorbidity, people having antibiotic exposure within 180 days before non-ICI systemic therapy had poorer cancer survival (hazard ratios ranging from 1.21 [95% confidence interval: 1.06–1.39] to 1.58 [1.34–1.87]) for shorter periods since antibiotic exposure (P < .0001). Similarly, poorer survival trends applied for localized and metastatic cancer. Of six prevalent cancers studied, lung and breast primaries showed the strongest associations of lower survival with prior antibiotic exposure. Conclusion: Antibiotic exposure within 180 days before non-ICI systemic cancer treatment is associated with poorer survival. If confirmed in other studies, it provides another reason for vigilant antibiotic stewardship.