(Reuters Health) – Women with obesity who undergo bariatric surgery may have a lower risk of breast cancer and get diagnosed at earlier stages when they do develop these malignancies, a recent meta-analysis and systematic review suggests.

Researchers examined data from 11 studies with a total of 1,106,939 women with obesity, including 105,295 women (9.5%) who underwent bariatric surgery. At baseline, the weighted mean BMI was similar for women in the bariatric surgery group (44.8) and the control group (44.6).

After a mean follow-up of 4.7 years in the bariatric surgery group, 567 (0.54%) invasive breast cancers were diagnosed. By comparison, after a mean follow-up of 2.7 years for the control group, 8,365 (0.84%) invasive breast cancers were diagnosed.

The risk of a breast cancer diagnosis was significantly lower in the bariatric surgery group (risk ratio 0.50) and so was the risk of stage III or IV cancer at diagnosis (RR 0.50). At the same time, women in the bariatric surgery group who were diagnosed with cancer had a significantly greater chance of being diagnosed with stage I cancer (RR 1.23).

“Without a doubt the most direct and substantial influence is simply from the large amount of weight lost and the subsequent decrease in circulating estrogens,” said senior study author Dr. Aristithes Doumouras, an assistant professor at McMaster University and a bariatric surgeon at St. Joseph’s Healthcare in Hamilton, Ontario.

“I think the take-home message is that obesity is not just a passive process but really an active disease that has broad-ranging negative effects on health and should be aggressively treated,” Dr. Doumouras said by email.

The study results add to evidence that the negative effects of obesity are not limited to cardiovascular disease and can also impact cancer development, Dr. Doumouras added.

Results were based on surgeries performed from 2008 to 2013, and may not be representative of current bariatric surgery approaches, the study team notes in the American Journal of Surgery.

The magnitude and maintenance of any weight loss wasn’t consistently measured across the smaller studies in the analysis, nor was the definition or determination of menopausal status. These factors were therefore not part of the analysis.

More importantly, there is the potential for a “healthy user bias” to influence which women underwent bariatric surgery, which might also predispose these women to a lower risk of breast cancer, the researchers point out.

At the same time, women with more severe obesity are less likely to undergo mammography screenings and other forms of preventive and routine medical care, said Dr. Andrea Stroud, an assistant professor of surgery at Oregon Health & Science University in Portland who wasn’t involved in the study.

However, the study results do suggest that obesity should be incorporated into breast cancer risk calculators, Dr. Stroud said by email.

“It is clear that maintaining a healthy weight is important to reduce risk and that individuals with obesity may reduce their risk by losing weight, with surgery or by other means,” Dr. Stroud said. “It is important for clinicians to recognize the strong association between obesity and cancer risk, which is specifically higher in women and with female-specific cancers.”

SOURCE: https://bit.ly/2PJq85W American Journal of Surgery, online March 17, 2021.

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