New Study Confirms Bariatric Surgery Lowers Cancer Risk in Women

Pam Harrison

October 18, 2017

Bariatric surgery has again been shown to lower cancer risk, including both obesity-related and non–obesity-related carcinomas, in severely obese women, but a similar benefit wasn't seen among men in a new retrospective observational cohort study.

"Bariatric surgery is currently the most effective intervention for weight loss and long-term weight maintenance," write Daniel Schauer, MD, University of Cincinnati, Ohio, and colleagues in their paper in in the Annals of Surgery.

"We found that bariatric surgery is associated with a lower long-term risk of cancer compared with carefully matched patients with severe obesity who did not get bariatric surgery," they add.

"Promoting intentional weight loss, especially through the use of bariatric surgery, may greatly reduce the risk of cancer among patients with severe obesity," they conclude.

Reduction of 40% in Obesity-Associated Cancers in Women With Bariatric Surgery

Noting that severe obesity, defined as a body mass index (BMI) ≥ 40 kg/m2, increased in the United States from 0.8% in 1960 to 7.7% in 2014, the investigators analyzed data from the Kaiser Permanente integrated health insurance and care delivery system to compare bariatric surgical candidates with well-matched counterparts who were also obese but did not undergo bariatric surgery.

Electronic health record (EHR) databases and registries were mined from January 2004 through December 2014 to identify a total of 22,198 surgical cases, over 80% of which were female. Patients had to have had a BMI of ≥ 35 kg/m2 and no history of any cancer before surgery.

A total of 66,481 control patients were selected from the same EHR database and carefully matched for demographics and clinical characteristics, including the presence of diabetes and hypertension.

The average follow-up time was longer in the bariatric surgery cases (47 months) than the controls (41 months; < .001).

Nevertheless, at a mean follow-up of 3.5 years, women who had undergone a bariatric surgical procedure had a 33% lower risk of developing any cancer during follow-up than matched controls (P < .001).

"Results were even stronger when the outcome was restricted to obesity-associated cancers," the investigators continue, where bariatric surgical candidates had a 41% lower risk of developing any type of obesity-related carcinoma compared with severely obese women who had not been treated surgically (P < .001).

Obesity-associated cancers include: pancreatic cancer, the risk of which was reduced by 54% among those who had bariatric surgery vs controls (P = .04); postmenopausal breast cancer, which was 52% lower among surgical candidates (P < .001); endometrial cancer, which was reduced by 50% (P < .001); and colon cancer by 41% (= .04).

Women who had undergone bariatric surgery were also 26% less likely than nonsurgical controls to develop cancers not related to obesity (P = .001).

"For men, there were no statistically significant reductions in cancer risk for any cancer type," the study authors report. But as they explain, men are most likely to die of prostate and lung cancer, neither of which is associated with obesity.

Variable Effect of Bariatric Surgery on Cancers Among Women and Men

In May of this year, investigators involved in the Swedish Obese Subjects (SOS) study similarly reported that bariatric surgery reduced the risk of female-specific cancers, including breast, endometrial, ovarian, and all other gynecological cancers as well as the overall incidence of cancer in women.

And in an earlier report from the SOS trial, in 2009 — the investigators reported that bariatric surgery reduced cancer risk in obese women but not in obese men (Lancet Oncol. 2009;10:653-662).

Dr Schauer and colleagues point out the variable effect of bariatric surgery on the incidence of obesity-related cancers but say this is "not surprising" given that cancer arises via multiple pathways.

For example, both postmenopausal breast and endometrial cancer are fueled by estrogen. By inducing significant weight loss, bariatric surgery reduces estrogen levels, thus reducing the risk of both cancers.

More research is needed to better understand the underlying mechanisms by which bariatric surgery reduces cancer risk, at least in women, they conclude.

Annals of Surgery. Published online September 21, 2017. Abstract

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