In this large, multisite cohort of patients with severe obesity, bariatric surgery was associated with a lower risk of incident cancer, particularly obesity-associated cancers, such as postmenopausal breast cancer, endometrial cancer, and colon cancer. More research is needed to clarify the specific mechanisms through which bariatric surgery lowers cancer risk.

Objective: This retrospective cohort study examined whether bariatric surgery is associated with reduced risk of breast cancer among pre- and postmenopausal women. Background: Obesity is associated with increased risk of breast cancer, but the impact of weight loss on breast cancer risk has been difficult to quantify. Methods: The cohort included obese (body mass index ≥35 kg/m2) patients enrolled in an integrated health care delivery system between 2005 and 2012 (with follow-up through 2014). Female bariatric surgery patients (N = 17,998) were matched on body mass index, age, study site, and comorbidity index to 53,889 women with no bariatric surgery. Kaplan–Meier curves and Cox proportional hazards models were used to examine incident breast cancer up to 10 years after bariatric surgery. Pre- and postmenopausal women were examined separately, and further classified by estrogen receptor (ER) status. Results: The analysis included 301 premenopausal and 399 postmenopausal breast cancer cases. In multivariable adjusted models, bariatric surgery was associated with a reduced risk of both premenopausal (HR = 0.72, 95% CI, 0.54–0.94) and postmenopausal (HR = 0.55, 95% CI, 0.42–0.72) breast cancer. Among premenopausal women, the effect of bariatric surgery was more pronounced among ER-negative cases (HR = 0.36, 95% CI, 0.16–0.79). Among postmenopausal women, the effect was more pronounced in ER-positive cases (HR = 0.52, 95% CI, 0.39–0.70). Conclusions: Bariatric surgery was associated with a reduced risk of breast cancer among severely obese women. These findings have significant public health relevance because the prevalence of obesity continues to rise, and few modifiable breast cancer risk factors have been identified, especially for premenopausal women.

We have developed and validated a population-based risk scoring system for serious complications after bariatric surgery. We expect that this scoring system will improve the process of informed consent, facilitate the selection of procedures for high-risk patients, and allow for better risk stratification across studies of bariatric surgery.

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ObjectiveThe goal of this study was to determine whether the reduction in cancer risk after bariatric surgery is due to weight loss.MethodsWe 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.ResultsWe 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.ConclusionsWeight 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.