Colorectal cancer incidence is rising globally among individuals younger than 50 years and remains poorly explained by established risk factors. In this study, we advance the hypothesis that early-childhood exposure to mutagen-producing bacteria contributes to lifetime colorectal cancer risk by imprinting oncogenic mutations in the developing colorectal epithelium, thereby initiating tumorigenesis decades before clinical diagnosis and redefining early-onset colorectal cancer as a disease rooted in early-life mutagenic exposure.
©2026 American Association for Cancer Research.