Scientists have known for years that obesity can rise cancer risk, but how? Now, new research offers clues to how fat cells encourage tumors.
The issue is an important one, the study author said.
"Obesity is increasing dramatically worldwide, and is now also recognized as one of the major risk factors for cancer, with 16 different types of cancer linked to obesity," explained Cornelia Ulrich, of the Huntsman Cancer Institute in Salt Lake City.
To help prevent the disease, "we urgently need to identify the specific mechanisms that link obesity to cancer," she said.
Prior studies have already outlined several ways fat could play a role in cancer. For example, obesity increases inflammation in the body, which has long been associated with the disease.
Obesity can also affect cancer cell metabolism and undermine the immune system's natural defenses, which may help tumors to grow and spread.
Ulrich's team noted that the link between fat and cancer also hinges on cellular "crosstalk" -- changes in complex chemical signaling within cells. Finding ways to interrupt this "crosstalk" could lead to new ways to help prevent cancer, the researchers theorized.
In the new review, to be published Sept. 5 in Cancer Prevention Research, an international team of researchers looked at data from 20 existing studies. The studies were published over the past seven decades, and each focused on cellular crosstalk between fat cells and malignant tumors.
In several of these studies, certain fat cells -- known as "adipose stromal cells" -- were able to invade cancer lesions and then help spur the growth of tumors. The data also showed that obese people with prostate or breast cancer appeared to have more of these cells than thinner people.
Some types of fat cells are also more "metabolically active," releasing more substances that promote tumor growth, the review found.
Also, fat may be white, brown or beige, Ulrich's team noted. And these different types of fat each behave differently, depending on quantity and location in the body. For example, the review found that white fat tissue is linked with inflammation and worse outcomes for women with breast cancer.
The location of fat in the body also influences how it affects certain types of cancer, the review found. Fat tissue is usually adjacent to colon and rectal cancers, the research team noted, and it is part of the direct environment of breast tumors.
According to the team, future studies might help doctors figure out if it's possible to disrupt the processes that promote the growth of tumors by affecting nearby fat.
"We are just beginning to unravel the ways crosstalk occurs and the substances involved," Ulrich said in a journal news release. "The more we understand this process, the better we can identify targets and strategies for decreasing the burden of obesity-related cancer."
Two experts in obesity agreed that this type of research is important.
"Obesity is going to surpass cigarette smoking as the leading cause of cancer deaths," said Dr. Mitchell Roslin, chief of obesity surgery at Lenox Hill Hospital in New York City.
"The take-home message here is that proper nutrition and maintaining a proper weight is essential for successful preventative health," he said. "Obesity is not inert and impacts virtually every aspect of your body, and not in a positive manner."
Dr. Raymond Lau is an endocrinologist at NYU Winthrop Hospital in Mineola, N.Y. He said that "there has long been an association between obesity and cancer risk. There is growing evidence that inflammation is the common link between these two disease states, and this review article helps to strengthen this relationship."
The U.S. National Cancer Institute provides more information on risk factors for cancer.
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