Oral Antibiotic Use in Adulthood and Risk of Early-Onset Colorectal Cancer: A Case-Control Study

Prior antibiotic use may be a factor in the rising incidence of colorectal cancer seen in those under 50 years of age (early-onset colorectal cancer [EOCRC]); however, the few studies to examine this link have reported conflicting results. Therefore, we evaluated the association between oral antibiotic use in adulthood and EOCRC in a large integrated healthcare system in the United States. A population-based nested case-control study was conducted among Kaiser Permanente Northern California patients 18–49 years of age diagnosed with EOCRC (adenocarcinoma of the colon or rectum) in 1998–2020 who had ≥2 years of continuous pharmacy benefit prior to diagnosis. Cases were matched 4:1 to healthy controls on birth year, sex, race and ethnicity, medical facility, and duration of pharmacy benefit. Antibiotic exposure >1 year before the diagnosis/index date was assessed using prescribing records. Conditional logistic regression was used to estimate odds ratios and 95% confidence intervals. A sensitivity analysis was performed among those with ≥10 years of continuous prescribing records. A total of 1359 EOCRC cases were matched to 4711 healthy controls. Antibiotic use in adulthood was not significantly associated with EOCRC in unadjusted or adjusted analyses (adjusted odds ratio, 1.04; 95% confidence interval, 0.94–1.26). No associations were seen for cumulative number of oral antibiotic dispensations or for any prior period of antibiotic exposure. In a large U.S. healthcare setting, there was no conclusive evidence of an association between oral antibiotic use in adulthood and risk of EOCRC.