Weight-loss surgery cut the incidence of breast and colon tumors by 85% and 70%, researchers say.
The study confirms the findings of two papers issued in August that showed the surgery reduced overall deaths from cancer. The new study goes a step further by showing reductions in the incidence of several specific types of cancer, said Dr. Philip Schauer of the Cleveland Clinic Lerner College of Medicine, who was not involved in the study.
“This is really powerful information,” said Schauer, immediate past president of the American Society for Metabolic and Bariatric Surgery. “It reaffirms that obesity is a profound risk factor for cancer” and shows that “weight loss does seem to affect the development of new cancers.”
But Dr. Edward H. Phillips, a bariatric surgeon at Cedars-Sinai Medical Center, was skeptical about the findings because cancer takes a long time to develop and the patients were studied for only five years.
He noted that it was now common for weight-loss surgery candidates to undergo mammograms, colonoscopies and endoscopies to screen for cancer before the procedure.
“It could be that we are selecting people out of the population who don’t have cancer,” biasing the results, Phillips said. He believes that losing weight will reduce the incidence of cancer but that it will take longer than five years for the effects to surface.
Christou countered that such screening “is not the standard of care” in Canada, where the subjects lived. Furthermore, many of the patients had undergone surgery as long as 15 years before the start of the study, he said, leaving plenty of time for cancer to develop.
There are two main types of bariatric surgery. The simpler is banding, in which an inflatable silicone band is placed around the stomach to reduce its capacity, allowing the patient to feel full after eating much less food.
In a gastric bypass, the stomach is sewn shut to reduce its capacity to 3 or 4 ounces, and the intestines are connected directly to the newly created pouch, bypassing part of the area where food absorption occurs. This is generally a more invasive surgery but produces greater weight loss.
About 205,000 Americans underwent bariatric surgery last year, according to the American Society for Metabolic and Bariatric Surgery, and the number is expected to rise by 5% this year. Only about 1% of those eligible for the surgery opt to undergo it, the society said.
Christou and his colleagues compared 1,035 patients who had had bariatric surgery between 1986 and 2002 with 5,746 carefully matched obese patients who had not had the surgery; 81% of the surgery patients had undergone a gastric bypass.
Neither the patients nor the controls had previously been diagnosed with cancer.
Those who underwent the surgery lost an average of 67% of their excess body weight.
In the five years of follow-up, the team observed 21 cancer cases in the surgery group (2%), compared with 487 cases (8.5%) in the control group, Christou told a Washington meeting of the American Society for Metabolic and Bariatric Surgery.
The most dramatic decreases were for breast and colon cancer. The researchers also observed a 70% reduction in pancreatic cancer, a 60% reduction in skin cancer, a 15% reduction in uterine cancer and a 50% reduction in non-Hodgkin’s lymphoma, but there were not enough cases of any of these for the results to be statistically significant.
Combined with earlier evidence, Christou said, “the data is pretty convincing” that weight loss reduces the incidence of cancer. “We looked at extreme weight loss, where we were more likely to pick it up. But any weight loss, if it can be maintained, is likely to improve the risk of cancer.”
Nobody knows how weight reduction reduces the incidence of cancer, said Dr. Peter LePort, director of the MemorialCare Center for Obesity in Fountain Valley, who was not involved in the study. But fat is known to secrete estrogen, which plays a crucial role in breast and some other cancers, he said.
The surgery may alter the production of other hormones as well. “What’s really needed here are a couple of studies to confirm the results and explore the mechanisms,” LePort said.
Despite evidence for the efficacy of the surgery, insurance companies have been “throwing subtle roadblocks” in front of patients seeking it, said Dr. Jeremy Korman, director of the Los Angeles Bariatric Center in Marina del Rey.
Some insurers require patients to try a medically supervised diet for six to 12 months before the surgery will be covered, although a recent survey found that most patients have been on an average of 24 diets before seeking surgical help.
“The hoops and hurdles are so onerous that patients give up before surgery,” Hutcher said.
Dr. Lisa Latts, a vice president at Anthem Blue Cross, cautioned that “the reality is that it is very important to pick the right patients. The wrong patients can out-eat bariatric surgery and undergo a very costly and dangerous procedure for nothing.”
Data from the Michigan Bariatric Surgery Collaborative presented earlier this month showed that the rate of life-threatening events during the surgery was 0.5%, down from 2% in 2000.