Bariatric surgery lowers risk for breast cancer among women with higher insulin levels
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Key takeaways:
- Women with obesity who underwent bariatric surgery were less likely to develop breast cancer than those receiving usual care.
- Reduced risk for breast cancer was observed among those with higher baseline insulin.
Women with obesity who undergo bariatric surgery and have higher levels of insulin have a lower risk for breast cancer than women who do not undergo surgery, according to findings published in JAMA Surgery.
“There are retrospective studies suggesting that bariatric surgery reduces breast cancer risk and this was one of the motivations to perform this study,” Felipe M. Kristensson, MD, a PhD student and resident physician in the department of molecular and clinical medicine at University of Gothenburg in Sweden, told Healio. “The Swedish Obese Subjects study is a prospective intervention study and one of the few prospective studies were these associations can be explored why we wanted to utilize the study.”
Researchers conducted a secondary analysis of data from the Swedish Obese Subjects study, where morbidity and mortality outcomes for adults aged 37 to 60 years with obesity who had bariatric surgery were compared with a control group of adults who received usual care. Participants were enrolled from Sept. 1, 1987, to Jan. 31, 2001. The secondary analysis included 2,867 women with a BMI of 38 kg/m2 or higher at baseline (mean age, 48 years). Baseline examinations were conducted 4 weeks before surgery. Follow-up occurred at 6 months and 1, 2, 3, 4, 6, 8, 10, 15 and 20 years. Blood samples were collected at 2, 10, 15 and 20 years. Breast cancer events were obtained from the Swedish Cancer Registry up until Dec. 31, 2020.
There were 1,420 women who had bariatric surgery and 1,447 women in the usual care group. Of those who underwent surgery, 68.3% had vertical banded gastroplasty, 18.3% underwent gastric banding and 13.4% had gastric bypass.
During a median follow-up of 23.9 years, 66 breast cancer events occurred in the surgery group and 88 in the usual care group. In adjusted analysis, there was no difference in risk for breast cancer between the two groups. However, when breast cancer events from the first 3 years of the study were excluded, women who underwent bariatric surgery had a lower risk for breast cancer than women receiving usual care (adjusted HR = 0.67; 95% CI, 0.47-0.95; P = .02). Among premenopausal women, bariatric surgery was associated with a lower breast cancer risk than usual care (aHR = 0.64; 95% CI, 0.42-0.99; P = .045), but no association was found among postmenopausal women.
The median baseline insulin level in the study group was 15.8 µIU/L. Among women with a baseline insulin level above the median, those who underwent bariatric surgery had a lower risk for breast cancer than those receiving usual care (aHR = 0.55; 95% CI, 0.35-0.86; P = .008). There was no difference in breast cancer risk between the two groups among women with a baseline insulin level below the median.
“Several observations support a role of insulin in the development or progression of breast cancer,” the researchers wrote. “Insulin stimulates cell mitosis and inhibit apoptosis, and overexpression of insulin receptors is common in breast cancer cells. Hyperinsulinemia has been linked to poorer outcomes in women with breast cancer. Furthermore, high levels of insulin are associated with reduced production of sex hormone-binding globulin and increased levels of bioactive estrogen, contributing to the development of breast cancer.”
Kristensson said future research should examine whether the risk for breast cancer following bariatric surgery differs among subtypes.
“Furthermore we aim to further explore the impact of bariatric surgery on cancer incidence for other cancers as well and if insulin may affect treatment effect,” Kristensson said. “On a separate note, further studies are needed to explore the mechanism by which insulin may affect cancer development.”
For more information:
Felipe M. Kristensson, MD, can be reached at felipe.kristensson@gu.se.
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