The recent information from Imperial College Medical School London concerning the possible use of aspirin in the prevention of prostate cancer confirms early data. Work by Professor Angus Dalgleish and Dr Ken O'Byrne has postulated a theory as to the mechanisms involved.

Professor Angus Dalgleish of St George's Hospital, London concluded from reports published on patients taking aspirin over many years, that they had a lower rate of cancer, including colorectal, lung cancer and oesophageal cancer. To this might now be added prostate cancer. One in three people develop cancer at some in their life so that treatment or prevention has been a primary target of medical research for decades. In theory, the body's own immune system should seek out and destroy cancerous cells which are constantly produced as the result of genetic damage.

This self-protective system does not always happen. The new theory which ties the spread of cancer to the failure of the immune system to stop the spread of the disease, was first proposed in a lecture which Professor Angus Dalgleish gave in 1999. He showed that studies of the immune systems of colon cancer patients highlighted unusually low levels of so called Th1-type immunity normally associated with the destruction of bacteria.

He believed that this permitted the cancer to thrive and believed that Th1 (thymus-derived helper cell type 1) was present in low levels as a result of inflammatory disease being tackled by the body's immune system. Professor Dalgleish's lecture was given at Leicester Royal Infirmary and Dr Ken O'Byrne, who was working at Leicester on how tumours spread, saw how this permitted a lot of questions to be answered.

Cancer starts when healthy cells are attacked over a long period by irritants such as chemicals from smoking. Long-term inflammation occurs and the body's immune system attempts to eliminate this. The Th1 level is lowered. Th1, apart from its work on cancer cells is needed by the body to deal with viruses and bacteria. When Th1 levels are low, normal cells that have become cancerous can multiply because the immune system is compromised.

In addition Dr O'Byrne believes inflammation triggers the wound healing process which increases the so-called Th2 response. This is involved in the creation of new blood vessels around damaged tissue in normal healthy conditions. If however the tissue is cancerous, the blood vessels make it easier for the cancer to grow and spread.

In effect, long-term tissue inflammation not only lowers Th1 levels allowing cancer cells to develop undetected but increases the Th2 level encouraging growth and spread. Inflammatory conditions such as ulcerative colitis and chronic hepatitis are linked to cancer in later life. It is the immune system's involvement with the inflammatory process which allows cancer cells to thrive. Drugs that fight inflammation therefore raise Th1 levels so that cancer can be targeted or even prevented. "aspirin is an obvious case in point", said Dr O'Byrne.

The linking of cancer with inflammation could lead to the development of drugs which reduce inflammation in order to frustrate the development of cancer. The theory has attracted interest from many leading experts in cancer control including Professor Adrian Harris of the Imperial Cancer Research Fund who said that, "To spread, tumours have got to get a blood supply and escape immune surveillance.

This new approach gives two routes for dealing with that." Professor Dalgleish believes that a big clinical trial is needed to test this new approach involving thousands of patients over several years. All the same, he himself is so convinced of the link between inflammation and cancer that he is taking 300mg of soluble aspirin daily but emphasises that such a course should only be undertaken with medical supervision.

Editorial footnote:
The Aspirin Foundation is organising a scientific conference at the Royal College of Surgeons in Ireland on Wednesday November 1 st. One of the speakers at this conference will be Dr Katherine Sheehan working now at the Beaumont Hospital in Dublin. The title of her paper is Cox-2 Inhibition in the Treatment of Cancer.