Early trials of the drug, named Zarnestra, suggest it benefited a quarter of patients in whom conventional treatment had failed.

Even though death rates from breast cancer have fallen sharply over the past decade, it remains one of the biggest killers of women in the UK, claiming more than 10,000 lives a year.

While this drug did not cure women, it appeared to delay the cancer's progress - and may yield a longer life to some.

Quarter success

Trials were carried out at the Royal Marsden Hospital in London in conjunction with the Institute of Cancer Research.

In total, 76 patients - most of whom had already undergone several cycles of chemotherapy and hormone treatment - were given the drug in tablet form.

Tumours either shrank back, or stopped growing, in up to a quarter of these.

It is very early days, but our hope for patients is that they will add further benefit to our current conventional treatments

Dr Stephen Johnston, Royal Marsden Hospital

A new trial will now examine whether the drug gives even better results if delivered in tandem with hormone treatment.

Zarnestra works by interrupting a signalling system unique to cancer cells which is vital to their growth and development.

It is the the first of a series of similar "inhibitor" drugs under development at the institute.

Researcher Dr Stephen Johnston said: "This is one of several new drugs which have been designed to target key enzymes in breast cancer.

"It is very early days, but our hope for patients is that they will add further benefit to our current conventional treatments."

Professor Peter Rigby, the chief executive of the institute, said: "This clearly benefit of having a comprehensive cancer centre, like that formed by the institute and the Royal Marsden.

"By having scientists and clinicians working closely together we can speed up the development of new treatment."