Men with otherwise untreatable prostate cancer could halt its spread and survive longer by undergoing immunotherapy treatment, a trial has shown.

More than a third of men with an advanced form of the cancer were still alive and one-in-10 had not had further growth after a year on the drug pembrolizumab, the study found.

It is the first time immunotherapy has been shown to benefit some men with prostate cancer, the researchers said.

The trial of 258 men led by a team at the Institute of Cancer Research, London, and the Royal Marsden NHS Foundation Trust, will be presented at the American Society of Clinical Oncology annual meeting in Chicago.

Prof Johann de Bono, director of the drug development unit, said: “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.”

Immunotherapy drugs work by stimulating the immune system to recognise and fight the cancer. They are used to treat some advanced cancers, including lung.

The trial found the men lived much longer when treated with “checkpoint inhibitor” pembrolizumab. About 38% were still alive after a year and 11% did not see the cancer grow.

Previous trials using immunotherapy in prostate cancer have been unsuccessful but the latest research examined the genetics of the tumours and found particular groups of patients may benefit.

While only 5% of men in the trial saw their tumours shrink or disappear after treatment, many of those had mutations in genes involved in repairing DNA in their tumours.

The researchers suggest these mutating cancer cells may be easy for the immune system to recognise and attack because they look different from healthy cells.

Data from some other cancer types, such as bowel, has similarly shown tumours with defects in DNA repair mutations are more susceptible to immunotherapy.



De Bono said: “We are planning a new clinical trial, specifically in men with prostate cancer whose tumours have mutations in DNA repair genes, to see if immunotherapy can become a standard part of their treatment.

“It’s exciting that immunotherapy could offer some men more time with their loved ones where they have such advanced disease that they have run out of existing treatment options.”

Only about 20% of cancer patients respond to immunotherapy – something that researchers do not fully understand.

Prof Paul Workman, chief executive of the Institute of Cancer Research said: “Immunotherapy has proven to be a smarter, kinder treatment for many types of cancer but it still only works for a minority of patients.

“The challenges we now face are how to predict in advance who will benefit, and how to make immunotherapy work for more people.

“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.”

Research will now focus on identifying markers to help pick out the prostate cancer patients whose tumours are most likely to shrink after immunotherapy treatment.