A breast cancer drug has been used to double the survival of men with advanced prostate cancer, becoming the first successful precision medicine for the disease.

Doctors at the Royal Marsden Hospital who conducted the trial say the results amount to a “revolution” in prostate cancer care.

They conducted genetic testing on more than 4,400 patients to identify those with one or more of 15 types of DNA fault.

Those who qualified were given olaparib, a course of pills which is commonly used to treat breast and ovarian cancer but is not currently licensed for prostate cancer.

The men in the trial had already failed to respond to hormone therapy - currently the best treatment available - and their prognoses were poor.

However, their length of progression-free survival, the period during which the cancer does not get worse, increased on average from 3.6 to 7.4 months.

This shows that using DNA testing to match patients with already available drugs can “transform” the treatment of the most common type of male cancer, according to the researchers.

The trial, which is being presented at the European Society for Medical Oncology annual congress in Barcelona, coincides with a new study in the journal Nature which suggests that using genetic information to re-purpose unlicensed or “off-label” drugs could benefit around one-third of patients for whom standard therapies do not work.