Bariatric Surgery and Colorectal Cancer Risk: A Critical Narrative Review of Comparative Evidence and Clinical Implications

Bariatric surgery is often presented as cancer-preventive, but its association with colorectal cancer (CRC) is less clear than for other obesity-related cancers. This critical narrative review examined epidemiological studies, evidence syntheses, human mechanistic studies and guidance identified through targeted searches updated to 31 October 2026, separating comparisons with nonsurgical obesity care from comparisons with the general population. Most meta-analyses report inverse associations, but results depend on the estimator and study selection: two largely overlapping reviews reported a nonsignificant pooled hazard ratio (HR) of 0.88 (95% confidence interval [CI] 0.69–1.12), and HRs of 0.81 and 0.75 only after excluding one study. Persistent excess colon cancer risk relative to the general population does not by itself indicate harm from surgery. The Swedish Obese Subjects study found no significant adjusted association after a median 22.2 years, and an October 2026 Nordic cohort found none for colon or rectal cancer. Human mucosal findings diverge, and experimental data offer hypotheses rather than clinical proof. The magnitude and causality of any association remain uncertain, and no late postoperative hazard is established. Screening after surgery should follow established risk factors, prior colonoscopy findings and symptoms rather than the operation alone.