But Karin said perhaps the biggest surprise came in studies of mice on a high-fat diet who were given DEN a little later in life, when they were three-months-old. 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, Karin explained. But the obese mice developed the disease without that extra push.

"We expected to see more cancer in our first experiments, but I was stunned to see here that only the mice who were obese developed the cancer," Karin said. "Obesity appears to be as strong as phenobarbitol; we can conclude, at least in mice, that obesity is a real tumor promoter."

His team was able to trace the source of obesity's tumor-promoting effect to a rise in two inflammatory factors known as IL-6 and TNF. Obese mice lacking either the TNF receptor or IL-6 don't show the same rise in liver cancer.

Those treatments also led the mice to accumulate less fat in their livers, he said. "They still get fat, but the distribution of the fat is different," he said. "The fat goes to other places, but not to the liver."

Karin suggests that clinical studies of people who are already taking anti-TNF drugs should be done, to find out if their livers are less fatty and cancer-free.

Source: Cell Press