While being overweight appears to reduce breast cancer risk until perimenopause for reasons that are not well understood, gaining weight during adulthood increases the risk of postmenopausal breast cancer. However, even though overweight and obese women have a lower risk of premenopausal breast cancer, obesity appears to contribute to more aggressive forms of the disease when younger women do develop it. Now a new study has reported that bariatric surgery was more effective in reducing tumor size than weight loss achieved through diet in a mouse model of premenopausal basal-like breast cancer.

Latest research finds surgery is more beneficial than diet-based weight loss

The study referenced above was designed to compare the effects of surgical and non-surgical weight loss on tumor burden in a mouse model of premenopausal basal-like breast cancer. Basal-like breast cancer, an aggressive form of the disease, is most often triple negative (ER-/PR-/HER2-). However, not all basal-like tumors are triple negative and not all triple negative tumors are basal-like. Obesity is associated with increased risk of basal-like breast cancer. Population studies have produced conflicting results concerning whether weight loss offers protection against basal-like breast cancer in obese women—only significant sustained weight loss appears to produce a consistent anti-cancer benefit.

To conduct the study, the authors fed mice either a high-fat diet designed to induce obesity or a control diet for 15 weeks. At this point, half of the obese mice continued the obesity diet, and half underwent either a surgical or dietary weight loss intervention. The mice in the surgical group underwent sleeve gastrectomy in which approximately 70% of the stomach was removed, whereas those in the dietary weight loss group were put on a low-fat diet. Both groups of mice achieved body weights and body fat percentages similar to the mice in the control group. After the body weights had stabilized, all the mice in the study were injected with E0771 mammary tumor cells, which model basal-like breast cancer.

At the end of the study, the average tumor weight in mice that had received weight loss surgery was statistically equivalent to that of control mice that had maintained normal weight throughout the study. On the other hand, the average tumor weight in mice that had lost weight through diet was statistically equivalent to that of obese mice (both groups had significantly larger tumors than control mice). In addition, mice in the surgery group had lower circulating insulin and interleukin-6 compared to mice in the weight loss diet group and obese mice. This suggests that the sleeve gastrectomy more effectively reduced obesity-associated inflammation. The authors conclude that the anti-cancer benefit observed for bariatric surgery could be related to a significant reduction in systemic inflammation and growth factor signaling, which did not occur in mice with equivalent non-surgical weight loss.

Please see our article on obesity for more information.