An inflamed tissue is a melting pot of cancer-causing molecules

Professor Angus Dalgleish

However, a new report suggests that the importance of this role may have previously been under-estimated.

The authors argue that long-standing over-activation of the immune system is the key event in the genesis of many forms of the disease.

The research could herald an entirely new approach to both preventing and treating cancer.

Drug therapy

It raises the prospect that some existing anti-inflammatory drugs - currently front-line treatments for conditions like arthritis and inflammatory bowel disease - could be used to keep cancer at bay.

According to conventional wisdom, cancer has a variety of causes.

But Dr Ken O'Byrne, of the University of Leicester, and Professor Angus Dalgleish of St George's Hospital in London argue that many of these factors work in the same way - by switching on the immune system for too long.

Dr O'Byrne said: "One of the biggest mysteries of cancer is why the body allows cells to build up cancerous mutations, when it has an immune system that ought to stop this from happening.

"But we think that when the immune system overcooks, perhaps because of long-term exposure to an infection or carcinogenic chemical, it loses its ability to fight disease and instead may actually begin to nurture and protect young cancer cells.

"If we could calm the immune system down with certain anti-inflammatory drugs, we might be able to reduce the rates of many common cancers."

Kicked into action

This review makes a fascinating case for the link between exhausted immunity, chronic inflammation and cancer

Dr Mary Berrington

Tissues become inflamed when the immune system is kicked into action by injury, infection or an allergic reaction.

White blood cells and molecules involved in the immune response are produced to fight off infection and aid the healing process.

But the same molecules that stimulate the regeneration of damaged tissues may also play a part in the birth of cancer and accelerate its growth and spread.

The researchers argue that continually switching on the immune system encourages cancer in a number of ways:

• Immune cells that would normally kill developing cancer cells can be switched off.
• Immunity for healthy cells can be spread to cancer cells too.
• Blood vessel growth is stimulated, providing nutrition for cancer cells
• Many immune system molecules are extremely chemically reactive, and may actually cause cancerous mutations by attacking DNA.