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 on insulin have a lower risk for breast cancer than women who do not undergo surgery, according to findings published in JAMA Surgery.

“To our knowledge, this is the first prospective nonrandomized controlled trial indicating an association between bariatric surgery and reduced risk of breast cancer in women with obesity,” Felipe M. Kristensson, MD, a doctoral student in the department of molecular and clinical medicine at University of Gothenburg in Sweden, and colleagues wrote. “Our results are in line with previous retrospective studies, and in agreement with our previous study on female-specific cancer, we also show that the association between bariatric surgery and reduced risk of breast cancer is primarily observed in women with higher insulin levels at baseline.”



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Women with obesity who undergo bariatric surgery and have higher insulin levels are less likely to develop breast cancer than women not undergoing bariatric surgery. Image: Adobe Stock

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.”

Among the study’s limitations, researchers cautioned that breast cancer incidence was not a predefined outcome of the Swedish Obese Subjects study and said the findings in the study should be regarded as exploratory.

“Also, our study includes older surgical methods that are no longer used,” the researchers wrote. “However, vertical banded gastroplasty, the most commonly used method in our study, results in weight loss similar to that after sleeve gastrectomy. Since the protective effect of bariatric surgery on cancer risk appears to be related to the degree of weight loss, our results are likely to also be valid for surgical methods used today.”

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