Women with early stage breast cancer (cancer that has not spread beyond the breast or axillary lymph nodes) who gain weight after diagnosis have a less favorable prognosis than those who do not. This includes weight gain during treatment and after treatment has been completed. Losing weight through diet and exercise can improve a woman's hormonal profile. Breast cancer survivors who lose weight can reduce circulating estrogen, improve insulin resistance, and reduce markers of angiogenesis. However, while intentionally losing weight might improve the prognosis of triple negative (ER-/PR-/HER2-) survivors, it is not clear that it has the same beneficial influence on hormone receptive positive disease (ER+/PR+) disease. Now a new study has reported that weight loss surgery appears to greatly improve prognosis among breast cancer survivors.

Impact of conventional weight loss on breast cancer progression

Relatively few studies have focused on the impact of weight loss on breast cancer prognosis. This is partly because significant intentional weight loss during the first year after diagnosis is relatively rare. Also, any weight loss that does occur could be the result of as yet undetected metastatic disease. The few available animal studies suggest that intentionally achieving normal weight might not be sufficient to reverse the effects of long-term obesity on epigenetic reprogramming and inflammatory signals in the tumor microenvironment that promote breast cancer progression.

For example, two studies using mouse models of breast cancer have investigated whether losing weight could improve survival of initially obese breast cancer patients. The outcomes of obese mice and formerly obese mice who were implanted with tumor cells were compared to that of mice who had never been obese. Mammary tumor growth in the formerly obese mice was found to be significantly higher than in mice who had always been lean. This was despite the fact that the formerly obese mice had lost all of their excess weight before being implanted.

Latest research reports weight loss surgery linked to lower recurrence rates

The retrospective study referenced above was designed to investigate the impact of weight loss surgery (bariatric surgery) after breast cancer diagnosis on cancer-related outcomes. Bariatric surgery has been found to be associated with reduced breast cancer risk, but the question of the influence of post-diagnosis surgery on prognosis is still open. To conduct the study, the authors analyzed data concerning 53,575 breast cancer survivors between 2004 and 2017. Using insurance claims data, they identified claims for patients with at least one year of no breast cancer treatment before their bariatric surgery date. Controls with no history of breast cancer recurrence or bariatric surgery were matched to the cases. The controls were theoretically eligible for bariatric surgery (defined as having BMI ≥ 35 kg/m2 and not having any of 20 comorbid illnesses that would exclude them from eligibility). To capture instances of relapse, the authors identified the following events after bariatric surgery: chemotherapy; diagnosis of metastatic disease; or additional breast surgery. Study participants were followed for up to 11 years, with a median follow-up of three years.

The study included 108 bariatric surgery cases who had not experienced breast cancer relapse for at least one year before their surgeries. The relative risk of relapse among patients who had bariatric surgery was found to be 45% lower than the control group of obese breast cancer survivors who did not have the surgery. The authors conclude that bariatric surgery is associated with reduced risk of breast cancer relapse among obese breast cancer survivors compared to similar women who do not undergo bariatric surgery. This suggests that a randomized control trial of bariatric surgery compared to best medical management should be undertaken, according to the authors.

Please see our article on weight gain for more information.