An international trial led by The Institute of Cancer Research, London, and The Royal Marsden NHS Foundation Trust has shown that immunotherapy can benefit men with prostate cancer.

According to the researchers, a subset of men who had run out of all existing options for treatment “survived much longer than expected when taking immunotherapy”.

Of the 258 men taking part in the trial with advanced prostate cancer receiving MSD’s checkpoint inhibitor Keytruda (pembrolizumab), 38 percent were still alive after a year and 11 percent are still receiving the treatment 12 months after the trial began without seeing their cancer grow.

Just 5 percent of men in the trial saw their tumours actually shrink or disappear after treatment, but the proportion was higher in a small group of men whose tumours had mutations to genes involved in repairing DNA, the researchers noted.

As such, they intend to explore this finding in a further trial to determine whether there is a particular subset of prostate cancer patients that might benefit most from immunotherapy.

“In the last few years immunotherapy has changed the way we treat many advanced cancers – but up to now no one had demonstrated a benefit in men with prostate cancer. Our study has found that immunotherapy can benefit a subset of men with advanced, otherwise untreatable prostate cancer, and these are most likely to include patients who have specific DNA repair mutations within their tumours,” said Professor Johann de Bono, director of the Drug Development Unit at The ICR and at The Royal Marsden NHS Foundation Trust.

“One of the major challenges with immunotherapy is that we don’t have many reliable tests to pick out who will benefit,” added Professor Paul Workman, chief executive of The ICR.

“This new trial has found that testing for mutations in DNA repair genes could be valuable marker of who will respond. If we can prove that in the planned new trial, it should be possible to provide some men with advanced prostate cancer with an exciting new treatment option.”

The research was presented at the American Society of Clinical Oncology annual meeting in Chicago.