Cancer risk increased by bacterial infection
Long-lasting inflammation, such as that caused by persistent bacterial infections, is estimated to account for up to 16% of cancers worldwide. By studying stomach infection in mice, scientists are now starting to understand why this natural defence mechanism is inadvertently causing harm. Their research suggests that chemicals released by the body’s immune cells to fight infection build up over time, causing DNA damage and disease.
A bacterium called Helicobacter pylori causes inflammation, stomach ulcers and cancer in humans. Helicobacter hepaticus has a similar effect in mice, so the researchers used it as a model to study how such a bacterial infection alters genes and chemicals in the liver and colon. Ten weeks after infection the mice developed severe colitis and hepatitis (inflammation of the colon and liver), and at 20 weeks, some had also developed colon cancer. They found that the greater the inflammation, the greater the DNA damage, which in turn would increase cancer risk.
Further investigation revealed that immune cells called macrophages and neutrophils, which migrate to inflamed tissue to fight infection, release highly reactive chemicals to break down the infecting bacteria. These chemicals leaked into the surrounding tissue causing damage and over a long period of time this could cause cancer. The findings show how important it is to treat infections early and will help doctors in the diagnosis and prevention of cancer.