Nutritionist calculating body mass index of woman for obesity treatment in a clinic room. Current research shows the gut microbiome may also influence risk for obesity.
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Obese individuals who had weight loss surgery were about half as likely to develop certain types of cancer and more than a third less likely to die from the disease than those didn’t have the procedure, according to a new study presented at the recent American Society for Metabolic and Bariatric Surgery (ASMBS) Annual Meeting.

“We knew bariatric surgery would reduce cancer risk based on previous studies, but what surprised us was the extent of that reduction in certain cancers,” said study-co-author Jared R. Miller, MD, a general and bariatric surgeon at Gundersen Lutheran Health System. “The benefits of cancer risk reduction through weight-loss surgery cannot be ignored and should be a consideration for patients with obesity and at high risk for cancer.”

The study was a retrospective review of patients undergoing bariatric surgery between September 2001 through December 2019 at Gundersen Lutheran Health System, Wisconsin. Patients had a body mass index (BMI) greater than or equal to 30 prior to surgery.  It included 1,620 patients who had either gastric bypass surgery (1,265 patients) or sleeve gastrectomy (355 patients), and 2,156 patients matched based off of age, sex, and BMI, who did not have surgery. The researchers estimate surgery patients lost about 60% of their excess weight at 10 years.

The team found that weight-loss surgery patients saw big reductions in the incidence of breast cancer (1.4% vs 2.7%), gynecologic cancer (0.4% vs 2.6%), kidney cancer (0.10% vs. 0.80%), brain cancer (0.20% vs 0.90%), lung cancer (0.20% vs 0.60%), and thyroid cancer (0.10% vs 0.70%).

“A total of nine different cancer categories were covered in our study, and more than 20 subtypes of various cancers. A total of five out of nine different cancer categories had a statically significant reduction in cancer risk,” Miller told Inside Precision Oncology. “Some cancer subtypes, such as endometrial cancer, had a 12-fold cancer risk reduction, which was statically significant. Other cancers, such as lung cancer, had a relevant risk reduction, but it did not reach statical significance.”

The 10-year incidence of any new cancer in the bariatric group was also much lower (5.2% vs. 12.2%) and the 10-year survival rate was much higher (92.9% vs. 78.9%) than the non-surgical group.

Miller said, “There are a multitude of proposed mechanisms for obesity leading to cancer development. Mechanisms such as increased inflammation, increased adiposity leading to higher circulating estrogen levels, changes in epigenetics, and changes in gut microbiome (normal intestinal flora) have been described in the development of cancer.”

He added that, “It has been hypothesized that the weight loss after bariatric surgery may indeed influence these mechanisms.”

The US Centers for Disease Control and Prevention (CDC) estimates more than 650,000 obesity-associated cancers occur in the United States each year. From 2005 to 2014, most cancers associated with overweight and obesity increased 7%, while the rate of new cancers not associated with excess weight dropped by 13%. According to a 2014 position statement from the  American Society of Clinical Oncology (ASCO), obesity is a major unrecognized risk factor for cancer and is associated with worsened prognosis after cancer diagnosis.

“The data continues to mount – when you treat obesity, you prevent certain cancers,” said Shanu Kothari, MD, President, ASMBS, in a press release about these findings. Kothari was not involved in this study. “Weight-loss surgery has proven to be the most effective long-term treatment for obesity and now it’s increasingly being looked upon as a preventative treatment, not only for cancer, but heart disease, stroke and type 2 diabetes too,” he added.

In 2016, the ASMBS issued a position statement on the relationship between obesity and cancer, and the role of bariatric surgery and the impact of weight loss not only on cancer risk, but on survivorship after treatment.

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