A DRUG developed to treat cancer in dogs could also be effective in humans, a study by American scientists has found.

Doctors at the Harvard Medical School say that the experimental drug, SU11248, has shown potential against human cancers of the lung, breast and kidney.

It is also about to enter a large-scale trial in the United States for the treatment of gastrointestinal stromal tumours, a type of cancer that affects about 1,000 Britons a year.

Last month, doctors at Harvard reported that the drug shrank the tumours in 60 out of 90 people with gastrointestinal stromal cancer. Although they were not fully cured, their conditions improved and their lives were prolonged.

Dr George Demetri, an associate professor of medicine at Harvard, who led the research, said: "We are seeing major clinical benefits and are extremely excited about this drug. Eight to 10 per cent of patients have a miraculous response. The tumours virtually shrink away to nothing.

"In another 40 per cent, the tumours stop growing. This means we can extend people's lives for years, rather than months. Extending life is major progress."

The drug works by preventing a protein called VEGF from stimulating the growth of blood vessels. Tumours are reliant on the growth of blood vessels and without them quickly become starved of oxygen and nutrients. The drug has worked effectively on dogs for some years before its potential to help human cancer sufferers was explored and developed.

Pharmaceutical giant Pfizer, that is funding the development of SU11248, is planning a larger study. If successful, the company will seek a licence for commercial production.