Antibiotic exposure and cancer risk: an umbrella review elucidating the direction of risk across 14 malignancies

BACKGROUND: Antibiotics are among the most frequently prescribed medications worldwide. However, previous studies have yielded inconsistent findings regarding the association between antibiotic exposure and the risk of various cancers, and the credibility of the available evidence remains uncertain. METHODS: We conducted an umbrella review based on published meta-analyses and systematic reviews to evaluate the association between past or current antibiotic exposure and cancer risk. PubMed, Embase, Cochrane Library, and Web of Science were searched from inception to November 2025. Pooled effect sizes were obtained utilizing random-effects models. The credibility of evidence was evaluated utilizing the GRADE framework. All analyses were analyzed utilizing the R package "metaumbrella". RESULTS: 10 articles encompassing 14 cancer types and 66 distinct associations were included. 9 associations were classified as highly suggestive evidence, 7 as suggestive evidence, and 21 as weak evidence. Among associations for which the evidence reached the highly suggestive level, antibiotic exposure was associated with increased risks of proximal colon cancer, pancreatic cancer, kidney cancer, and bladder cancer. CONCLUSIONS: Antibiotic exposure may be related to cancer risk in a cancer type-specific manner. These findings provide a higher-level evidence synthesis to inform future research directions and hypothesis generation in this field.