By Kathleen Doheny
FRIDAY, June 13, 2014 (HealthDay News) -- Weight-loss surgery may do more than lower the risk of heart problems and improve type 2 diabetes in obese patients: A new review suggests it may also lower their chances of a cancer diagnosis.
"Bariatric surgery is associated with reduced cancer risk in morbidly obese people [to that of normal-weight people]," the team of Brazilian researchers wrote. Their report was published recently in the journal Obesity Surgery. A morbidly obese person is roughly 100 pounds overweight, with a body-mass index (BMI) of 40 or higher.
Cancer experts in the United States who reviewed the findings were not completely convinced that surgery can reduce cancer risk to that of normal-weight people. But they agreed that obesity raises the risk of certain cancers.
The Brazilian researchers, from the Hospital Sao Lucas in Porto Alegre and other institutions, pooled the results of 13 studies including more than 54,000 people. Each study looked at cancer rates after weight-loss surgery.
Cancer rates in obese people are as high as two per 1,000 person-years (the number of years times the number of people in a population affected by a certain illness).
However, in those who had the surgery, the researchers found the rate was about one per 1,000 person-years, or nearly that of normal-weight people. The follow-up ranged from two to 23 years after the surgery.
The risk reduction with weight loss surgery is "probably true," said Dr. Cy Stein, chair of medical oncology and experimental therapeutics at the City of Hope Medical Center in Duarte, Calif.
It would make sense, he said, since "the evidence that obesity is related to an increased risk of cancer is significant, even in the modestly obese. There is an association [between obesity and cancer]. It is a risk factor for cancer development."
According to the American Cancer Society, an estimated one of three cancer deaths in the United States is linked to excess weight, poor diet and/or inactivity. The link between weight and cancer is strongest, the society says, for breast cancer in women past menopause, colon and rectal cancers, and cancers of the esophagus, kidney, pancreas and uterine lining (endometrium).
Even so, another cancer expert who reviewed the finding recommended "taking it with a grain of salt and a little bit of hesitation."
"I would say overall the evidence appears [to show] there is a reduction in risk," said Lauren Teras, director of hematologic cancer research at the American Cancer Society. "It's just hard to say for certain."
Even the researchers suggest that the conclusion should be viewed with care, since the studies they reviewed differed in the way they were conducted, potentially affecting results. Also, the review was not designed to determine a cause-and-effect link.
How to explain the apparent association between obesity and cancer?
"I think there is some good evidence that hormones play a role," Teras said. For instance, fat tissue is the largest source of estrogen in women past menopause, and that is thought to be linked with the type of breast cancer that needs estrogen to grow.
Another possible connection, she said, is inflammation. As people gain more and more weight, they have an increase in inflammation, and that may help tumors grow and spread.
"We're not sure if the obesity causes the cancer," Stein said, "but it may promote it."
Teras offered one more caveat: "Weight-loss surgery, like any surgery, is not without risks. The risks and benefits should be weighed with a person's individual doctor."