Association between bariatric surgery and risks of cancer among Chinese patients with type 2 diabetes mellitus: A retrospective cohort study

Background To examine risks of cancers, obesity-related cancers (eg, cancers in digestive organs, breast, ovary, kidney, thyroid, and myeloma), cancer-related mortality, and all-cause mortality in patients with type 2 diabetes mellitus (T2DM) and obesity who underwent bariatric surgery. Methods A retrospective cohort of 1944 T2DM patients with obesity (345 bariatric surgery patients and 1599 matched controls) who were free of cancer from 2006 to 2017 was assembled. One-to-five propensity score matching followed by propensity score trimming was used to balance baseline covariates. Results During a mean follow-up period of 37 months, there are risks that in 3.2%, 1.4%, 0.9%, and 3.2% of bariatric patients cancer, obesity-related cancer, cancer-related mortality, and all-cause mortality, respectively, would occur. Surgical patients were found to have reduced incidence rates (IRs) of obesity-related cancer (0.531/100 person-years, 95% confidence interval [CI]: 0.172-1.238/100 person-years) and cancer of breast and genital organs (0.394/100 person-years, 95% CI: 0.048-1.424/100 person-years) than matched control patients whose IRs for obesity-related cancer and cancer of breast and genital organs were 0.627/100 person-years (95% CI: 0.426-0.889/100 person-years) and 0.521/100 person-years (95% CI: 0.277-0.891/100 person-years), respectively. Patients in the surgical group had a significant reduction in risk of all-cause mortality (hazard ratio [HR] = 0.508, P = .041). Effects of bariatric surgery on any cancers (HR = 1.254, P = .510), obesity-related cancers (HR = 0.843, P = .724), and cancer mortality (HR = 1.304, P = .694) were not significant. Conclusions Bariatric surgery was not associated with risks of overall cancer, obesity-related cancer, and cancer mortality among T2DM patients with obesity at 3 years.