Association between Antibiotic Use and Subsequent Risk of Breast Cancer: A Nationwide Retrospective Cohort Study in South Korea

Abstract Background Several studies have revealed a possible association between antibiotic use and breast cancer in the Western population of women. However, its association with the Asian population remains unclear. Methods Data utilized in this nationwide population-based retrospective cohort study was obtained from the Korean National Health Insurance Service (NHIS) database. The study population consisted of 4,097,812 women who were followed up from January 1, 2007, to December 31, 2019. Cox proportional hazards regression was utilized in order to calculate adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) for the risk of breast cancer according to cumulative days of antibiotic use and the number of antibiotic classes used, respectively. Results It was discovered that participants who used antibiotics for more than 365 days had a higher risk of breast cancer (aHR, 1.15; 95% CI, 1.09–1.21) in comparison to those who did not use antibiotics. In addition, a correlation was found among participants who utilized five or more classes of antibiotics in which they developed a higher risk of breast cancer (aHR, 1.11; 95% CI, 1.05–1.17) than those who were not antibiotic users. Conclusions Our research and findings propose that long-term antibiotic use may be associated with an increased risk of breast cancer when multiple covariates are taken into account. The findings support the epidemiological evidence that long-term use of antibiotics may be associated with the risk of breast cancer and demonstrate the need for further studies to confirm causation and mechanisms.