It offers fresh hope for patients who do not respond to current therapies.

Patients treated with the new drug irinotecan in separate trials in the UK and France lived longer and showed fewer symptoms of the disease than patients receiving other treatments.

One study compared the action of irinotecan with that of the current drug treatment while the other guaged the effectiveness of it in patients who had not previously responded to medication.

Prevalent cancer

Cancer of the colon is one of the most common adult malignant tumours and affects one person in 20 in Europe.

Surgery cures 40-50% of these, but in some cases the cancer has spread to other parts of the body - a condition known as metastatic cancer.

When this happens, patients are usually given chemotherapy to kill off the remaining cancer.

Surgery cures 40-50% of cases

With the current drug treatment, fluorouracil, patients usually survive for 10-12 months.

The new research, published in The Lancet medical journal, showed that irinotecan helped patients who did not respond to fluorouracil.

Dr David Cunningham, of the Royal Marsden Hospital, in London, led the UK study.

He said: "Our study shows that despite the side-effects of treatment, patients who have metastatic colorectal cancer, and for whom fluorouracil has failed, have a longer survival, few tumour-related symptoms, and a better quality of life when treated with irinotecan than with supportive care alone."

More than 36% of the 189 patients who received the drug in his trial survived to one year, compared to just 13.8% of the 90 patients who were only given emotional support but no drug treatment.

The main side-effect was severe diarrhoea.

Improved performance

In the French study doctors gave patients continuous infusions of irinotecan or fluorouracil.

The research was conducted by Dr Philippe Rougier, of the Institut Gustave-Roussy, Villejuif, and colleagues.

They found that patients who took irinotecan lived for 10.8 months of average compared to 8.5 months for people given fluorouracil.

Dr Michael O'Connell of the Mayo Clinic in Rochester, Minnesota, reviewed the research in The Lancet.

He said: "After nearly 40 years of clinical trials, there is now an active drug completely different in action from flourouracil for further study in patients with colorectal cancer."

However, irinotecan is expensive and Dr O'Connell stopped short of advocating the new drug as standard treatment.