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Undergoing bariatric surgery in order to lose weight may substantially reduce some patients’ risk of cancer, according to a new study.

The finding, which mirrored the results of some previous studies, relied on observational data and not a randomized controlled trial, the gold standard of scientific research. Still, Ali Aminian, lead author of the study and director of Cleveland Clinic’s Bariatric & Metabolic Institute, described the data as “striking.”


The new study, conducted at the Cleveland Clinic, included 5,053 adult patients with obesity who had bariatric surgery and 25,265 who did not but were matched to the first group by characteristics such as sex, age, body mass index, smoking status, state of residence, and presence of type 2 diabetes.

Between 2004 and 2017, 96 patients in the surgery group and 780 in the control group developed cancer. That translates to a rate of 2.9% in the bariatric surgery group and 4.9% in the control group – meaning that patients who received surgery appear to have developed cancer 32% less often. Over 10 years, 0.8% of the patients in the bariatric surgery group and 1.4% of those in the control group died from cancer, a 48% difference in the rate of death. The results were published Friday in the Journal of the American Medical Association.

“Patients in this study were very obese,” wrote Joanne Elmore, a professor of medicine at the David Geffen School of Medicine, in an email. She noted that a BMI of 45, the median level for a patient, equates to a person who is 5’8” and weighs 300 pounds. She also pointed out that patients who choose to undergo bariatric surgery could be very different from those who don’t, which could bias the results. For instance, perhaps patients who undergo the surgery are trying to be healthier in other ways. Still, she said: “This study provides yet another reason to increase our efforts to maintain a healthier weight.”


Otis Brawley, a Bloomberg distinguished professor at Johns Hopkins University, said the results, when combined with previous research, mean that at least for people who have a high body mass index, bariatric surgery has a clear benefit.

“I’m pretty certain that the weight reduction in people with a high BMI prevents some cancers and some cardiovascular disease,” Brawley said.

However, Brawley noted, the data are weaker for people who are obese but have lower BMIs. He noted that most obese Americans have a BMI in the high 30s, significantly lower than the median BMI of 45 seen in the study.

Most of the patients enrolled in the study were women, who are more likely to undergo bariatric surgery. The most pronounced effect, Brawley noted, was in uterine cancers, which are more closely linked to obesity. Obese women have a 12-fold higher risk of uterine cancer. However, the study also saw substantially lower rates of colorectal, prostate, and breast cancers.

Steven Nissen, the study’s senior author and the chief academic officer of the Cleveland Clinic’s Heart, Vascular, and Thoracic Institute, said in a statement that the study provides “the best possible evidence on the value of intentional weight loss to reduce cancer risk and mortality.”

The results could play a role in an ongoing discussion over whether obesity should be treated medically. That could influence how often and when insurance companies cover bariatric weight loss surgery. It could also influence how insurance companies cover new classes of drugs that can be used for weight loss. These medicines, originally developed to treat diabetes, are gaining traction as weight loss treatments. They include Wegovy, from Novo Nordisk, and terzepitide, a new medicine being developed by Eli Lilly. Nissen is working with Lilly on the obesity medicine.

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