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SOS: Breast cancer risk reduced after bariatric surgery in women with hyperinsulinemia

There is a reduced risk of breast cancer after bariatric surgery in women living with obesity and this reduced risk was predominantly seen in women with hyperinsulinemia, suggesting insulin may be used as a predictor of treatment effect. These are the latest findings from the landmark Swedish Obese Subjects (SOS) study.

The SOS study was a non-randomised intervention trial designed to investigate the long-term effects of bariatric surgery on obesity-related mortality and morbidity. Study recruitment took place between 1987 and 2001, and median (IQR) follow-up time was 23.9 years (20.1-27.1) years. The study was conducted at 25 public surgical departments and 480 primary health care centres in Sweden and included 2,867 women aged 37 to 60 years and with body mass index 38 or greater (calculated as weight in kilograms divided by height in meters squared).

In the surgery group (n=1420), 260 women underwent gastric banding, 970 vertical banded gastroplasty, and 190 gastric bypass. The remaining contemporaneously matched control individuals (n=1,447) received usual obesity care. The groups were otherwise comparable in terms of age and body composition.

Although breast cancer was the main outcome of this paper, it was not a predefined outcome in the SOS study, so breast cancer events were identified using data from the Swedish National Cancer Registry.


The results show that a total of 154 women developed breast cancer, 66 in the surgery group and 88 in the conventional obesity treatment group. Unadjusted analyses revealed that women who underwent bariatric surgery had a 32% lower risk of developing breast cancer.

Further analyses showed that women with high levels of insulin at the start of the study, defined as insulin above the group median, had a 52% lower risk of developing breast cancer after bariatric surgery, compared with the control group.

There were no significant differences in BMI during follow-up in participants with and without breast cancer diagnosis within the treatment groups. In an unadjusted analysis, bariatric surgery was associated with a reduced risk of breast cancer compared to usual care (p=0.02); however, the association was no longer significant after adjustment for age, BMI, alcohol, and smoking status (p=0.06).

"Guided by our results, we will have better knowledge of which individuals have the best effect of surgery and which may not experience such favourable outcomes. This facilitates a more personalized care, i.e. ensuring that each patient receives the most appropriate treatment for their condition," explained Felipe Kristensson, a PhD student at the Sahlgrenska Academy at the University of Gothenburg and a co-author of the study. "The results also reflect the biological mechanisms underlying cancer development in which insulin appears to play an important role. Further research into such mechanisms also paves the way for the development of new cancer treatments."

The findings were featured in the paper, ‘Breast Cancer Risk After Bariatric Surgery and Influence of Insulin Levels - A Nonrandomized Controlled Trial’, published in JAMA Surgery. To access this paper, please click here


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