Association between Weight Loss and the Risk of Cancer after Bariatric Surgery

OBJECTIVE: The goal of this study was to determine whether the reduction in cancer risk after bariatric surgery is due to weight loss. METHODS: We conducted a retrospective matched cohort study of patients undergoing bariatric surgery using data from a large integrated health insurance and care delivery system with five sites in four states. The study included 18,355 bariatric surgery subjects and 40,524 non-surgical subjects matched on age, sex, BMI, site and Elixhauser comorbidity index. Multivariable Cox proportional hazards models examined the relationship between weight loss at 1 year and incident cancer up to 10 years follow-up. RESULTS: We identified 1,196 incident cancers. The average one year post-surgical weight loss was 27% among patients undergoing bariatric surgery vs 1% in matched non-surgical patients. Percent weight loss at one year was significantly associated with a reduced risk of any cancer in adjusted models (HR 0.897, 95% CI 0.832–0.968, p=0.005 for every 10% weight loss) while bariatric surgery was not a significant independent predictor of cancer incidence. CONCLUSIONS: Weight loss after bariatric surgery was associated with a lower risk of incident cancer. There was no apparent independent effect of the bariatric surgery itself on cancer risk that was independent of weight loss.