The study was small, involving just over 1,000 surgically treated patients, and the follow-up was just five years.
But the findings are in line with other recent studies suggesting a reduction in cancer risk and mortality among obese patients who lose weight as a result of having weight loss surgery, says McGill University director of bariatric surgery Nicholas Christou, MD, PhD, who led the research.
The unpublished findings were reported Wednesday at the 25th Annual Meeting of the American Society for Metabolic and Bariatric Surgery (ASMBS) in Washington, D.C.
"I think we can say with reasonable confidence that weight loss is associated with a reduced risk of cancer and death from the disease in morbidly obese people," Christou tells WebMD. "The weight loss doesn't have to be from surgery, but surgery is proving to be the only the permanent treatment option that we have for this group of patients."
Weight Loss and Cancer Risk
Last year, an estimated 205,000 people in the U.S. had gastric bypass, gastric banding, or some other form of bariatric, or weight loss, surgery.
Candidates for bariatric surgery include those who are morbidly obese, which for most people means being 100 or more pounds overweight or having a body mass index (BMI) of 40 or more.
A 5-foot, 5-inch person who weighs 245 or more would be considered morbidly obese, as would someone who is 6 feet tall and weighs at least 295 pounds.
The newly reported study included 1,035 morbidly obese patients who underwent bariatric surgery between 1986 and 2002 and 5,746 patients matched for age, gender, and duration of morbid obesity who did not have surgery.
During five years of follow-up, 21 (2%) surgically treated patients were diagnosed with cancer, compared to 487 (8.5%) of nonsurgically treated patients.
The bariatric surgery patients had an 85% lower incidence of breast cancer, a 70% lower incidence of colon and pancreatic cancer, a 50% lower incidence of non-Hodgkin's lymphoma, and a 60% lower incidence of skin cancer.
But because of the small study size, all but the breast cancer finding could have been chance findings, Christou says.
"With breast cancer we can be reasonably certain that the reduction was not due to chance," he says. "The other cancers were certainly trending in that direction, suggesting that there is something here that needs to be investigated further."
Obesity Linked to Many Cancers
Eugenia Calle, PhD, who studies the impact of obesity on cancer for the American Cancer Society, agrees that more research is needed to understand the role of weight loss and weight loss surgery in reducing cancer risk.
Calle tells WebMD that the list of cancers now recognized as being influenced by obesity is both long and growing.
Calle says patients who have had weight loss surgery offer a unique opportunity to study the impact of losing weight on cancer risk.
"It has not been easy to examine weight loss and how it influences cancer, because people don't generally lose a lot of weight and if they do they don't often keep it off," she says. "But this is not true of patients who have bariatric surgery."
No matter how you do it, maintaining a healthy weight is shaping up to be a critical component of cancer prevention, she says.
"After avoiding tobacco, weight control, eating a healthy diet, and staying physically active may be the most important things people can do -- and weight control is probably the most important of the three," she says.
"There is every reason to think that people who lose excess weight and maintain that weight loss -- no matter how they do it -- are going to have a lower risk of cancer going forward."