Bariatric Surgery May Prevent Breast Cancer in Obese Women

Researchers examined the relationship between women’s incidence of breast cancer and bariatric surgery in a recent study that was published in JAMA Surgery. They also looked into whether baseline insulin levels affected the benefit of bariatric surgery on breast cancer risk.

Context
One of the most prevalent cancers in women and a major contributor to cancer-related mortality is breast cancer. One of the main risk factors for breast cancer is obesity, which is also on the rise worldwide and worsens the course of the disease. One cellular growth factor that modifies the risk of cancer in fat is insulin.

Effective in lowering insulin levels and helping patients lose weight, bariatric surgery has been linked to a lower risk of cancer overall, especially malignancies that affect women. Although retrospective studies indicate that bariatric surgery lowers the risk of breast cancer, more investigation is required to confirm this finding and determine the underlying molecular causes.

Concerning the study

A total of 4,047 obese subjects, aged 37 to 60, with a body mass index (BMI) of 34 or higher for males and 38 or higher for women, were enrolled in the current Swedish Obese Subjects (SOS) study. Sweden was the location of participant recruitment from 1987 to 2001. A matched control group of 2037 patients received standard care, while the surgical group comprised 2010 participants receiving various bariatric operations.

Blood samples and questionnaires were used in the baseline and follow-up exams, which were carried out at various intervals for up to 20 years. The Swedish Cancer Registry was used to identify breast cancer events, and ICD-7 (International Classification of Diseases, Seventh Revision) code 170 was used for analysis. There were 1,420 women in the surgery group (260 with gastric banding, 970 with vertical banded gastroplasty, and 190 with gastric bypass), whereas there were 1447 women in the usual care group.

Kaplan-Meier estimates, Cox proportional hazards models, and t-tests were used in statistical analyses to compare therapy groups for breast cancer risk. Baseline age, BMI, alcohol consumption, and smoking status were all adjusted for. Subgroup studies assessed the impact of metabolic factors and insulin on the risk of breast cancer. Menopause and undetected baseline breast cancer were taken into account in sensitivity analyses. R and Stata were utilized in the analyses.

Study findings

2,867 women with a mean (SD) age of 48.0 (6.2) years made up the study population. Out of 17 parameters, 12 revealed significant differences between the baseline characteristics of the surgery group (n = 1420) and the usual care group (n = 1447). Compared to the surgery group, a greater percentage of women in the usual care group were menopausal at baseline (36.6% vs. 30.5%, respectively; P = 0.001).

After two, ten, fifteen, and twenty years of follow-up, the mean BMI changes in the surgery group were 10.4, 7.7, 7.5, and −7.8, respectively. During follow-up, the usual care group’s BMI changed very little.

There were 154 breast cancer incidences over a median follow-up of 23.9 years, with 66 occurring in the surgery group and 88 in the standard care group (log-rank test: χ12 = 5.63; Probability Value (P) = 0.02).

Among participants receiving treatment, there were no appreciable variations in BMI between those who had been diagnosed with breast cancer and those who had not.

Bariatric surgery was linked to a lower risk of breast cancer than usual care, according to unadjusted analysis (Hazard Ratio (HR), 0.68; 95% Confidence Interval (CI), 0.49-0.94; P = 0.02). However, this association did not hold true when age, BMI, alcohol use, and smoking status were taken into account (adjusted HR, 0.72; 95% CI, 0.52-1.01; P =.06).

There was no breach of the proportionate hazard assumption (adjusted P =.16). The connection held significance even after breast cancer events were eliminated during the first three years of study enrollment (adjusted HR, 0.67; 95% CI, 0.47-0.95; P = 0.02).

Breast cancer incidence was higher in the usual care group compared to the surgery group when stratified by menopausal status at baseline. This difference was observed after adjustment (adjusted HR, 0.64; 95% CI, 0.42-0.99; P = 0.045) for premenopausal women but not for postmenopausal women (adjusted HR, 0.84; 95% CI, 0.49-1.45; P = 0.54).

The median baseline insulin level (15.8 μIU/L) was used to stratify the cumulative incidence of breast cancer. Five were not included because their insulin data was unavailable.

For female patients with insulin levels above the median, the benefit of surgical therapy was larger. Insulin and therapy had a significant interaction (χ12 = 5.11; P = 0.02). Results remained unchanged when early breast cancer events were excluded.

The benefit of surgical treatment was also substantially correlated with the homeostasis model assessment-estimated insulin resistance (HOMA-IR) (χ12 = 4.82; P = 0.03). There were no observed interactions between the therapy and any risk variables. Results were comparable when early breast cancer events were excluded, with the exception of blood glucose (χ12 = 4.25; P = 0.04).

In summary

In conclusion, bariatric surgery is linked to a lower incidence of breast cancer in obese women, particularly in those whose initial insulin levels are high. This implies that insulin levels could be a useful predictor of the breast cancer-prevention efficacy of bariatric surgery.

For more information: Breast Cancer Risk After Bariatric Surgery and Influence of Insulin Levels: A Nonrandomized Controlled Trial, JAMA Surg, doi:10.1001/jamasurg.2024.1169