Bariatric surgery appears to have a protective effect on the risk of breast cancer in women with obesity, especially those with hyperinsulinemia, according to data from the Swedish Obese Subjects (SOS) study.
SOS included 2,867 women between 37 and 60 years of age (mean 48.0 years) with a body mass index of at least 38 kg/m2. Of these, 1,420 women underwent bariatric surgery, specifically gastric banding in 260, vertical banded gastroplasty in 970, and gastric bypass in 190. The remaining 1,447 received usual obesity care and served as controls.
The main study outcome of breast cancer incidence was ascertained using the Swedish National Cancer Registry. Over a median follow-up of 23.9 years, 154 breast cancer events were recorded, including 66 in the surgery group and 88 in the usual care group.
In multivariable analysis, bariatric surgery was associated with a 28-percent reduction in the risk of breast cancer (adjusted hazard ratio [HR], 0.72, 95 percent confidence interval [CI], 0.52–1.01; p=0.06).
The breast cancer risk-lowering benefit with bariatric surgery was especially pronounced in women with baseline insulin levels above the median value of 15.8 μIU/L (adjusted HR, 0.55, 95 percent CI, 0.35–0.86; p=0.008) compared with those whose baseline insulin levels were below the median value (adjusted HR, 1.01, 95 percent CI, 0.61–1.66; p=0.97; p=0.02 for interaction).