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October 17, 2012

Study Shows How Obesity Heightens Cancer Risk

by Jessica Berman

In addition to being a known risk factor for diabetes, morbid obesity causes higher death rates in severely overweight cancer patients, regardless of their diet. Scientists have new evidence that excess fat stimulates and supports tumor growth.

Experts say up to 25 percent of cancer cases occur in morbidly obese individuals. And, for reasons not fully understood, tumors appear to be more aggressive and therapy less effective in patients with excess fat tissue.

But researchers at the University of Texas Health Science Center at Houston may have found the reason at the molecular level. They say expanding fat tissue cells emit hormones and growth factors, called adipokines, that promote the growth of new blood vessels which nourish and promote tumor growth.

“What we hypothesized is that cells from fat tissue become mobilized and travel to the site of the cancer and become a component of the tumor.  And then those trophic factors, the adipokines, start being secreted from within the tumor.  And because of that, they are more potent because they are in higher concentration inside the tumor,” said Mikhail Kolonin, an associate professor of stem-cell medicine at U.T. Health’s Institute for Molecular Medicine.

In experiments with obese and lean mice with tumors, Kolonin's team fed each group of rodents the same diet. The tumors inside the fat mice grew much faster.  In addition, investigators discovered the growths inside the obese mice drew in the circulating fat cells. While many of the cells turned into fat inside the tumor, others promoted formation of the blood vessel network, bringing it oxygen and nutrients.

Kolonin says significant weight loss can reduce the presence of these tumor-inducing fat cells.  And  he believes performing gastric bypass or bariatric surgery in morbidly obese individuals is a fast and effective way to reduce their risk of cancer.

“It is apparent from studies that have been done that treating obesity before cancer onset may be very beneficial because bariatric surgery, for instance, prevents not only the risk of developing diabetes but also developing certain cancers,” Kolonin said.

Such cancers, common in the morbidly obese, include colorectal cancer and cancer of the prostate in men and endometrial cancer, a type of uterine tumor, in women.

An article by Mikhail Kolonin and colleagues on the links between obesity and cancer is published in the journal Cancer Research.