• Posted June 8, 2022

Weight-Loss Surgery May Greatly Lower Odds for Many Cancers

Dropping a load of pounds through weight-loss surgery can significantly decrease your risk of developing or dying from cancer, according to three new studies.

Obese folks who underwent bariatric surgery were at least two times less likely to develop certain types of cancer and more than three times less likely to die of cancer than heavy people who didn't get the procedure, according to a study presented Tuesday at the American Society for Metabolic and Bariatric Surgery's (ASMBS) annual meeting, in Dallas.

Another much larger study by the Cleveland Clinic found similar, if smaller, benefits from weight-loss surgery -- a 32% lower risk of developing cancer and a 48% lower risk of cancer-related death, according to results published June 3 in the Journal of the American Medical Association.

People need to lose at least 20% of their body weight to gain this protection against cancer, a goal that's far beyond the reach of people trying to shed pounds through diet and exercise, said lead researcher Dr. Ali Aminian, director of the Cleveland Clinic's Bariatric and Metabolic Institute.

"Most patients with lifestyle change only cannot reach that threshold," Aminian said. "I think this study suggests that instead of just focusing on lifestyle modification to reduce the risk of cancer, we need to use effective treatments for obesity."

The new studies' findings make sense, said ASMBS President Dr. Shanu Kothari said.

"We've known that people who undergo weight-loss surgery live longer compared to folks who qualify for the surgery but don't have it," Kothari said. "The main reason is they have fewer heart attacks, but now we're seeing they're also having fewer cancers. That's why they live longer."

Obesity tied to 13 cancers

More than 42% of Americans are obese, according to the U.S. Centers for Disease Control and Prevention. Their excess weight increases the risk of developing 13 types of cancer that account for two out of five cancers diagnosed every year in the United States.

In fact, obesity is expected to soon outstrip smoking as the world's top risk factor for developing cancer, given the global obesity epidemic, Aminian said.

For the first study, a Wisconsin team of researchers compared more than 2,100 bariatric surgery patients to more than 5,500 obese people who qualify for the procedure but didn't get it, according to a report at the ASMBS meeting.

Weight-loss surgery resulted in large 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%), researchers found.

During a decade-long follow-up, the weight-loss surgery group also had a much lower incidence of any new cancer (about 5.2% vs. just over 12%) and a higher survival rate (93% vs. 79%).

"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 researcher Dr. Jared Miller, a general and bariatric surgeon at Gundersen Lutheran Health System in La Crosse, Wis.

The Cleveland Clinic study involved even more patients, more than 5,000 who underwent weight-loss surgery versus more than 25,000 who didn't, according to the report in the Journal of the American Medical Association.

After 10 years, 3% of patients in the bariatric surgery group and 5% of the non-surgery group developed an obesity-related cancer, researchers found. About 0.8% of surgery patients and 1.4% of non-surgery people died from cancer.

Analysis showed that weight loss has a dose-dependent relationship to cancer risk -- the more weight you lose, the lower your cancer risk, Aminian said.

Another study presented on Tuesday at the ASMBS meeting also found that bariatric surgery reduced the risk of colon cancer by 37%.

This study combined data from 13 previous studies on weight-loss surgery that followed more than 3.2 million patients for as long as 10 years, said researcher Dr. Michal Janik, a general and bariatric surgeon at the Military Institution of Aviation Medicine in Warsaw, Poland.

Previous studies had suggested that bariatric surgery might increase the risk of colon cancer, but this large-scale analysis found the opposite was true, Janik said.

"We found something that was contrary to those earlier studies, because we performed a very detailed analysis of all studies," Janik said.

Bariatric surgery is currently the only way to achieve the sort of weight loss needed to prevent cancer, Aminian and his colleagues argue.

Clinical trials have shown that intensive diet and exercise can lead to an average weight loss of nearly 9% within a year, they said in background notes.

Pounds need to stay off

The researchers agreed that the weight needs to stay off for the cancer protection to keep steady, and argued that at this point weight-loss surgery provides the most durable benefits.

However, Aminian noted that new drugs under development might soon help people drop enough pounds to provide similar protection against cancer.

"There are new medications in the pipeline that can help patients get to that 20% to 25% weight loss," Aminian said. "And if those medications become available to patients and accessible to the public, then we should see the same results."

Fat cells promote many risk factors for different types of cancer, Miller said, including systemic inflammation and elevated levels of the hormones insulin and estrogen.

"We believe that bariatric surgery through weight loss is indirectly affecting all these different mechanisms, thus decreasing the incidence of cancer and reducing the risk of cancer, Miller said.

Findings presented at medical meetings are considered preliminary until published in a peer-reviewed journal.

More information

The U.S. National Cancer Institute has more on obesity and cancer.

SOURCES: Ali Aminian, MD, director, Cleveland Clinic Bariatric and Metabolic Institute, Cleveland, Ohio; Shanu Kothari, MD, president, American Society for Metabolic and Bariatric Surgery; Jared Miller, MD, general and bariatric surgeon, Gundersen Lutheran Health System, La Crosse, Wis.; Michal Janik, MD, general and bariatric surgeon, Military Institution of Aviation Medicine, Warsaw, Poland; Journal of the American Medical Association, June 3, 2022