These latter three are caused by the destruction of the white blood cells that normally fight infections, and they can often result in major problems; if accompanied by a fever, death will ensue within hours or even minutes. Indeed, many cancer patients may have actually been killed by chemotherapy, and not the disease (J Clin Oncol, 1997; 15: 3320-9).

A new chemotherapy drug called irinotecan (marketed by Upjohn as Camptosar) has recently come into use, intended for patients who don't respond to 5-FU. However, studies show that, like 5-FU, Camptosar's benefits are limited, extending survival by about three months compared to no treatment at all but with all the attendant side effects (Lancet, 1998; 352: 1413-8). Chemotherapy has also been found to be useless in treating metastases in the liver the most common result of colon cancer (Arch Med Res, 1998; 29: 319-24).

Gene therapy, although heavily trumpeted in the media, is in reality a distant hope, as oncologists will admit among themselves.

First stage trials are currently underway in animals, but already concerns are being raised over toxicity, side effects and lack of ability to target specific tumours (Hematol Oncol Clin North Am, 1998; 12: 595-615).

Screening tests

Because of such poor outlooks for colorectal cancer patients, the official line is that people should be encouraged to have regular check ups to detect the cancer before it takes hold, particularly those individuals who are at high risk (see box, p 1). However, in practice there are many problems in carrying through this advice. First, the warning signs of the cancer (iron deficiency anaemia, rectal bleeding, change in bowel movements, abdominal pain and weight loss) tend to become noticeable only when the cancer is already well established.

Second, the diagnostic tests themselves are sometimes not reliable. The simplest test, called the occult blood test, measures blood in the faeces but is notoriously prone to false positive results and, more importantly, false negatives. The more complex barium enema fares little better.

The more reliable tests, such as sigmoidoscopy and colonoscopy (visualisation of different areas of the colon with a lighted tube inserted in the anus) are invasive, discouraging patients from undergoing routine checks. Further more, experience has also shown that even these sometimes fail to detect pre cancerous polyps (Ann R Coll Surg Eng, 1998; 80: 246-8). Finally, if all patients who were at risk were to demand routine check ups, neither private nor state run systems would be able to cope. But as the US National Cancer Institute admits, "limiting screening or early cancer detection to only high risk groups would miss the majority of colorectal cancers" (PDQ Statement, June 1999).

Prevention

For many oncologists, the major hope for the future of colon cancer lies in prevention. Some see a bright prospect for drugs as preventive agents after it was unexpectedly observed that aspirin, which is a non steroidal anti inflammatory drug (NSAID), reduced the incidence of colorectal cancer. A major clinical trial is currently underway in Europe, testing daily aspirin doses as high as 350 mg among patients who have undergone surgery to remove benign colorectal polyps.

An epidemiological study has also been completed on other NSAIDs. In 100,000 Americans aged over 65 who had been taking NSAIDs for conditions like arthritis, two year usage of the drugs reduced colon cancer risk by nearly 50 per cent, and one year usage, by about 40 per cent (Arch Intern Med, 1999; 159: 161-6). The authors predict similar results will be found with aspirin.