Bariatric Surgery and the Risk of Cancer in a Large Multisite Cohort

Abstract

Objective: To determine whether bariatric surgery is associated with a lower risk of cancer.

Background: Obesity is strongly associated with many types of cancer. Few studies have examined the relationship between bariatric surgery and cancer risk.

Methods: We conducted a retrospective cohort study of patients undergoing bariatric surgery between 2005 and 2012 with follow-up through 2014 using data from a large integrated health insurance and care delivery systems with 5 study sites. The study included 22,198 subjects who had bariatric surgery and 66,427 nonsurgical subjects matched on sex, age, study site, body mass index, and Elixhauser comorbidity index. Multivariable Cox proportional-hazards models were used to examine incident cancer up to 10 years after bariatric surgery compared to the matched nonsurgical patients.

Results: After a mean follow-up of 3.5 years, we identified 2543 incident cancers. Patients undergoing bariatric surgery had a 33% lower hazard of developing any cancer during follow-up [hazard ratio (HR) 0.67, 95% confidence interval (CI) 0.60, 0.74, P < 0.001) compared with matched patients with severe obesity who did not undergo bariatric surgery, and results were even stronger when the outcome was restricted to obesity-associated cancers (HR 0.59, 95% CI 0.51, 0.69, P < 0.001). Among the obesity-associated cancers, the risk of postmenopausal breast cancer (HR 0.58, 95% CI 0.44, 0.77, P < 0.001), colon cancer (HR 0.59, 95% CI 0.36, 0.97, P = 0.04), endometrial cancer (HR 0.50, 95% CI 0.37, 0.67, P < 0.001), and pancreatic cancer (HR 0.46, 95% CI 0.22, 0.97, P = 0.04) was each statistically significantly lower among those who had undergone bariatric surgery compared with matched nonsurgical patients.

Conclusions: 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.

Figure 1.

Cohort consort for bariatric surgery patients and the matched non-surgical controls.

Figure 2.

Kaplan-Meier Estimated Cancer-Free Survival for All Cancers (A), Obesity-Associated Cancers (B), and Cancers not Associated with Obesity(C). In panel A, there were 488 cancers in the bariatric surgery group and 2,055 cancers in the matched controls. For the obesity-associated cancers in panel B, there were 246 cancers in the bariatric surgery group and 1,185 in the matched controls. In panel C, there were 242 cancers not associated with obesity in the bariatric surgery group and 872 among the matched controls. The log rank test had a p-value of <0.001 for all three comparisons. The number at risk is the same in each panel because patients were censored at the first cancer regardless of the type.

Figure 2.

Kaplan-Meier Estimated Cancer-Free Survival for All Cancers (A), Obesity-Associated Cancers (B), and Cancers not Associated with Obesity(C). In panel A, there were 488 cancers in the bariatric surgery group and 2,055 cancers in the matched controls. For the obesity-associated cancers in panel B, there were 246 cancers in the bariatric surgery group and 1,185 in the matched controls. In panel C, there were 242 cancers not associated with obesity in the bariatric surgery group and 872 among the matched controls. The log rank test had a p-value of <0.001 for all three comparisons. The number at risk is the same in each panel because patients were censored at the first cancer regardless of the type.

Figure 2.

Kaplan-Meier Estimated Cancer-Free Survival for All Cancers (A), Obesity-Associated Cancers (B), and Cancers not Associated with Obesity(C). In panel A, there were 488 cancers in the bariatric surgery group and 2,055 cancers in the matched controls. For the obesity-associated cancers in panel B, there were 246 cancers in the bariatric surgery group and 1,185 in the matched controls. In panel C, there were 242 cancers not associated with obesity in the bariatric surgery group and 872 among the matched controls. The log rank test had a p-value of <0.001 for all three comparisons. The number at risk is the same in each panel because patients were censored at the first cancer regardless of the type.

Figure 3.

Forest Plot of Multivariable Cox Proportional Hazards models for Obesity-Associated Cancers. The box represents the hazard ratio and the error bars depict the 95% confidence interval. Matching occurred on age, sex, BMI, Elixhauser comorbidity index score and study site. The models are adjusted for race, diabetes, hyperlipidemia, hypertension, coronary artery disease, peripheral vascular disease, nonalcoholic steatohepatitis, a history of smoking, alcohol use, and use of hormone replacement therapy.