Until now, most anti-cancer drugs have caused unwanted side effects, because as well as attacking the cancer they attack healthy cells nearby. A new approach to drug development offers the potential for more effective treatment, avoiding or greatly reducing side effects because the drugs specifically target the cancer cells and do not affect healthy cells.

Several drugs are already being marketed in the US which can attack a particular molecule which encourages cancer,’ says Karol Sikora, Professor of Cancer Medicine at Hammersmith Hospital London. He predicts that by 2010 many more effective drugs will treat breast, lung, colorectal and prostate cancers.

Each of these new categories of drugs is suitable for treating only a very clearly defined cancer or group of cancers. One of these new categories is signal transductase inhibitors. These work by blocking a signal sent out by a faulty chromosome which could otherwise cause a cancer.

One of the first signal transductase inhibitors is Glivec (imatinib), which has recently been licensed for treatment of chronic myeloid leukaemia (CML). It has been tested in 10,000 patients in 30 countries. The National Institute for Clinical Effectiveness (NICE) is appraising Glivec. The Department of Health has made it clear that in the meantime all patients who could benefit from the new drug should be given it.

‘It’s very exciting,’ says Gareth Morgan, Professor of Haematology at Leeds University. ‘This is one of the first examples of a proper targeted drug treatment in leukaemia – or any cancer. It specifically inhibits the underlying defect leading to that cancer.‘ It heralds ‘a whole new generation of drugs that can actually kill the cancer, but not make your hair fall out.

In practice, patients have found the improvement caused by the treatment starts immediately,’ Professor Morgan adds. In clinical trials, up to 91 per cent of patients have had their white blood cell counts return to normal. Research is continuing to find out what effect Glivec has on patients’ survival.

Glivec works by stopping chemical reactions that cause over-production of immature white blood cells. Glivec identifies the faulty receptor and sticks to it, which stops it from stimulating the cells to grow (see diagram).

Glivec is also being used in trials for other types of leukaemia, and researchers are investigating its role in other cancers.