Aspirin, a medication used to treat pain, fever or inflammation, could significantly reduce the effects of obesity on cancer, suggests a study on mice. Obesity is a known risk factor for certain types of cancer, including colon, pancreatic and breast cancer. The new study, from Hokkaido University in Sapporo, Japan, showed that obesity could enhance cancer development by slowing down the key cancer defence mechanism. "Epithelial" cells lining the surfaces of organs have the intrinsic ability to remove potentially malignant cells from their midst. This is called the "epithelial defence against cancer" mechanism. Normally, the cells sense harmful cells and push them out by the process called cell competition. "This is the first report to show that obesity and chronic inflammation can influence competitive interaction between normal cells and transformed cells," said lead author Yasuyuki Fujita. "It implies other factors such as infection, smoking, sleeping patterns and ageing may also affect cell competition," Fujita added. To study how obesity affects this defence mechanism, the team bred mice that were designed to express a known cancer-inducing mutant protein called Ras. Epithelial cells usually remove the potentially malignant Ras-transformed cells. Feeding the Ras mice high-fat diets, which resulted in severe obesity, suppressed the defence mechanism and therefore increased the number of Ras-transformed cells remaining in the tissue. This suppression was seen in the intestine and pancreas, but not in the lungs, the researchers noted. A month later, the Ras-transformed cells developed a tumour in the pancreas of mice with the high-fat diet. Further experiments using the mice model and cultured cells revealed that fatty acids and chronic inflammation cause the suppression of the defence mechanism. However, when mice fed a high-fat diet were treated with aspirin, known for its anti-inflammatory properties, the defence mechanism was substantially enhanced. This implies that reinforcing the epithelial defence mechanism with anti-inflammatory drugs could be utilised for cancer prevention, the researchers said.