British scientists have announced that Olaparib, the first drug that targets precise genetic mutations in prostate cancer, has been shown to be effective in a “milestone” trial.

The study, at the Institute of Cancer Research in London, took place on 49 men with untreatable cancer.

Olaparib had low overall success, but slowed tumor growth in 88% of patients with specific DNA mutations.

Cancer Research UK said the trial was exciting.

Olaparib, the first marketed drug to tackle inherited cancer mutations, was licensed in 2014 for women with ovarian cancer who have faulty BRCA genes.

The future of cancer medicine is treating cancers by their mutated DNA rather than what part of the body they are in.

The breast cancer drug Herceptin is already used only in patients with specific mutations. Olaparib targets mutations that change the way DNA is repaired.

The trial results, published in the New England Journal of Medicine, showed the drug worked in 14 out of 16 men with such mutations.

Levels of Prostate Specific Antigen (PSA), which is produced by tumors, was more than halved and there were also significant falls in the number of prostate cancer cells detected in the blood and in the size of secondary tumors.

Patients responded to the drug for between six months and nearly a year and a half.

Prostate cancer is the fifth most deadly type of cancer in men.

However, a larger clinical trial is needed before doctors can say if the drug extends life expectancy.