Individuals with obesity were at least two times more likely to develop certain types of cancer and 3.5 times more likely to die from from the disease than those who had weight-loss surgery, according to a new study presented here today at the American Society for Metabolic and Bariatric Surgery (ASMBS) Annual Meeting (#ASMBS2022).

Researchers found that after having 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%).

The 10-year incidence of any new cancer in the bariatric group was 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. The retrospective study included 1,620 patients who had either gastric bypass surgery (1,265 patients) or sleeve gastrectomy (355 patients) between Sept. 2001 and Dec. 2019, and 2,156 patients matched based off of age, sex, and body mass index (BMI), who did not have surgery. Researchers estimate surgery patients lost about 60% of their excess weight at 10 years.

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. 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."

Jared R. Miller, MD,  study-co-author, general and bariatric surgeon at Gundersen Lutheran Health System

The U.S. 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 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.

Overweight and obesity can cause changes in the body that could lead to cancer, including long-lasting inflammation and high insulin levels. The risk of cancer increases the more excess weight a person gains and the longer they have overweight or obesity.

"The data continues to mount – when you treat obesity, you prevent certain cancers," said Shanu Kothari, MD, President, ASMBS, who was not involved in the 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."

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.