[Press and Publications] Scientists Inflame Debate on Cancer's Genesis



August 2001

No. 105

Long-term over-cooking of the immune system causing tissues to inflame and blood vessels to grow may be the single most important cause of cancer, according to a controversial report in this week's British Journal of Cancer.

Although many scientists agree that inflamed tissues may play a role in cancer, the authors go much further, arguing that long-standing over-activation of the immune system is the key event in the genesis of many forms of the disease.

Their research could herald an entirely new approach to both preventing and treating cancer, with 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, including inherited genetic errors, infections and exposure to chemicals and UV radiation. But Dr Ken O'Byrne of the University of Leicester and Prof Angus Dalgleish of St George's Hospital, London argue that many of these factors work in the same way by switching on the immune system for too long.

Dr O'Byrne says: "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."

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 pour into the tissue from the blood supply and lymphatic system, while many other molecules are produced by the tissue itself.

These molecules are designed to fight off infection and to help the body heal as quickly as possible. 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.

According to O'Byrne and Dalgleish, an immune system that is continually switched on encourages the genesis of cancer in a number of different ways:

  • Paradoxically, over-activation of the immune system sometimes actually switches off the immune cells that would normally kill developing cancer cells. The immune system then fails to notice when cancer develops.
  • Immunity, as well as killing viruses, bacteria and abnormal cells, is also designed to protect healthy cells, keeping them alive, encouraging them to divide and allowing them to move to areas where tissues need replenishing. But in some circumstances, an over-activated system can be perfect for looking after cancer cells too, encouraging them to grow and spread.
  • As part of the healing process, the immune system stimulates the growth of blood vessels. These provide regenerating tissue with a plentiful supply of oxygen and nutrients, and are also perfect for feeding hungry cancer cells.
  • Many immune system molecules are extremely chemically reactive, and may actually cause cancerous mutations by attacking DNA.
  • Dalgleish and O'Byrne believe that nearly all carcinogens work by over-cooking the immune system. As examples, they cite tobacco smoke and HPV, the virus that causes cervical cancer, both of which can cause long-term inflammation.

    And in a final, bizarre twist, not only may inflammation cause cancer, but cancer might cause inflammation too. The researchers think that the most successful cancer cells are those that are able to exactly mimic inflammatory conditions, in order to help themselves grow and spread.

    Professor Dalgleish says: "An inflamed tissue is a melting pot of cancer-causing molecules, so what better way for a cancer cell to give itself a helping hand that by learning to copy those very same conditions? Of course this means that some anti-inflammatory pills might not only help in preventing cancer, but in treating the disease too."

    Dr Mary Berrington, Science Information Manager for The Cancer Research Campaign, which publishes the British Journal of Cancer, says: "This review makes a fascinating, if not novel, case for the link between exhausted immunity, chronic inflammation and cancer. Itís essential that we look at all the evidence, although much of it at the moment is circumstantial."

    For media inquiries please contact Professor O'Byrne on 0116 258 7602, The Cancer Research Campaign's press office on 0207 487 3768 or mobile 07836 229 208 or mobile 07768 992 023. University of Leicester Press Office: 0116 252 3335.

    NOTE TO EDITORS:

    Not all inflammatory conditions encourage cancer. Diseases such as asthma do not contribute to the development of the disease.


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