A gene-targeting pill for women may provide a highly effective treatment for up to a third of men with advanced prostate cancer, trial results have shown.
Olaparib, the first marketed drug to tackle inherited cancer mutations, was licensed last year for women with ovarian cancer who have faulty BRCA genes.
The new trial, described as a "milestone" by the UK's Institute of Cancer Research, found it could also halt tumour growth in many men with treatment-resistant prostate cancer.
Of the 49 men taking part, a third responded to the drug. Cancers stopped growing, numbers of circulating tumour cells in the blood fell and clinically positive results were obtained from scans.
Levels of PSA - the blood marker used to track the progress of prostate cancer - also plunged by up to 96 per cent.
Chief investigator Professor Johann de Bono, from the Institute of Cancer Research, said: "We can detect prostate cancers with specific targetable mutations using genomic sequencing to deliver more precise cancer care by matching treatment to those men most likely to benefit."
Sixteen patients had detectable faults in genes that play a role in repairing damaged DNA, including BRCA 1 and 2. Of these, 14 responded very well to olaparib.
A second stage of the trial is now planned that will only recruit men with prostate cancer who have similar detectable gene defects.
If this study also yields positive results, olaparib could become a new treatment option for men with genetically driven advanced prostate cancer, say the researchers.
Women with breast cancer and defective BRCA genes are also known to respond to olaparib.
The new findings are published in the New England Journal of Medicine.
In 84 per cent of prostate cancer cases, patients live 10 or more years, but once the disease has spread and stopped responding to hormone treatments, the chances of survival are much slimmer.
Dr Aine McCarthy, from Cancer Research UK, said: "This trial is exciting because it could offer a new way to treat prostate cancer by targeting genetic mistakes in cancers that have spread."
Dr Iain Frame, director of research at Prostate Cancer UK, said: "These results demonstrate just how much we can benefit from the success of treatments for other disease."
The research received support from the Movember Foundation, which raises funds and cancer awareness by promoting the growth of moustaches.
