Obesity strongly promotes tumor growth in the liver
Researchers have identified a link between obesity and an increased risk of developing cancer, according to a study published in the journal Cell (2010;140:197-208).
To demonstrate how obesity plays a role in tumor promotion, researchers focused on hepatocellular carcinoma (HCC), a common form of liver cancer whose occurrence and progression among all cancers are most strongly affected by obesity. The team was able to trace the source of obesity's tumor-promoting effect to an influx of two inflammatory factors, IL-6 and TNF.
When 2-week-old mice were exposed to DEN, a chemical carcinogen, and then assigned to two different groups, one fed normal, relatively low-fat food and the other fed on high-fat food, mice on the high-fat diet developed more liver cancer. In addition, mice carrying an obesity-prone gene that were given DEN and fed a normal diet also developed more liver cancers, confirming that the obesity state, rather than the high-fat diet, led to the development of cancer.
More surprising to the researchers was that when mice on a high-fat diet were given DEN a litter later in life, the obese mice developed the disease without the addition of phenobarbitol. “Normally, mice on the standard diet given the chemical at that age really don't develop liver cancer unless DEN exposure is followed up with phenobarbitol,” explained Michael Karin, PhD, the study leader.
“We expected to see more cancer in our first experiments, but I was stunned to see here that only mice who were obese developed the cancer,” Dr Karin stated. “Obesity appears to be as strong as phenobarbitol; we conclude, at least in mice, that obesity is a real tumor promoter."