Long-term incidence of female-specific cancer after bariatric surgery or usual care in the Swedish Obese Subjects Study

Objective: To examine the long-term effects of bariatric surgery on female-specific cancer in women with obesity.

Methods: The prospective, matched Swedish Obese Subjects (SOS) study was designed to examine outcomes after bariatric surgery. This study includes 1420 women from the SOS cohort that underwent bariatric surgery and 1447 contemporaneously matched controls who received conventional obesity treatment. Age was 37-60years and BMI was ≥38kg/m². Information on cancer events was obtained from the Swedish National Cancer Registry. Median follow-up time was 18.1years (interquartile range 14.8-20.9years, maximum 26years). This study is registered with ClinicalTrials.gov, NCT01479452.

Results: Bariatric surgery was associated with reduced risk of overall cancer (hazard ratio=0.71; 95% CI 0.59-0.85; p<0.001). About half of the observed cancers were female-specific, and the incidence of these were lower in the surgery group compared with the control group (hazard ratio=0.68; 95% CI 0.52-0·88; p=0.004). The surgical treatment benefit with respect to female-specific cancer was significantly associated with baseline serum insulin (interaction p value=0.022), with greater relative treatment benefit in patients with medium or high insulin levels. Separate analyses of different types of female-specific cancers showed that bariatric surgery was associated with reduced risk of endometrial cancer (hazard ratio=0.56: 95% CI 0.35-0.89; p=0.014).

Conclusions: In this long-term study, bariatric surgery was associated with reduced risk of female-specific cancer, especially in women with hyperinsulinemia at baseline.

Funding: This project was supported by grants from the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under Award Number R01DK105948 (the content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health), the Swedish Research Council K2013-99X-22279-01, K2013-54X-11285-19, Sahlgrenska University Hospital ALF research grant and Swedish Diabetes Foundation.