This is for the first time that an immunotherapy has shown to be beneficial for men who suffer with prostate cancer that is responsible for the death of more people in the United Kingdom than the breast 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 fix mutations within their tumours", said Johann de Bono, Director of the Drug Development Unit at the Institute of Cancer Research.
The results will bring hope to men such as BBC presenter Bill Turnbull, 62, who in March revealed that he had been diagnosed with prostate cancer which had spread "to the bone".
"Our study provides prospective evidence that there might be inherited genes that could affect treatment response and track with African ancestry in prostate cancer patients", George said. The drugs alter the body's immune system that focuses directly on tackling cancer.
The world's leading expert on prostate cancer Professor Johann de Bono from the Institute of cancer research said: "We hope for a revolutionary cure, but they can't call it".
"African-Americans have a 2.5 times greater chance of dying from prostate cancer compared to whites", said Daniel George, M.D., director of Duke's Prostate & Urologic Cancer program, who presented the findings at the 2018 annual meeting of the American Society of Clinical Oncology in Chicago. We have several patients who have had a complete response.
He added: "This will be another arrow to the quiver for a subset of prostate cancers and the results are preliminary but very promising".
Two years ago, he was given the immunotherapy drug pembrolizumab.
"This is important as although immunotherapy is exciting, it can have severe side effects".
"One of the major challenges with immunotherapy is that we don't have many reliable tests to pick out who will benefit". It will then have to be assessed by the National Institute for Health and Care Excellence to see if it is cost-effective enough for prostate NHS cancer patients to receive it.
He says he's now planning out the next 20 years of his life, not the next two.
But now results from the ongoing Circulating Cell-Free Genome Atlas study, also presented at ASCO, offer hope of much earlier diagnosis - and so better survival.
The tests picked up nearly 90 per cent of late-stage cancers.
Professor Geoffrey Oxnard, of the Dana-Farber Cancer Institute in the U.S., said: 'The beauty of a blood test is it could just be done in a local GP office'.