A genetic test could help doctors identify prostate cancer patients who may benefit from immunotherapy, researchers say.
Scientists found tumours in a small group of men with an advanced form of the disease had a distinctive pattern of genetic changes.
The biological features of these tumours could mean they are more likely to respond to immunotherapy drugs such as pembrolizumab, according to a study published in journal Cell.
In the future, a test could help pick out men with these genetic changes so they can be considered for the treatment, the authors said.
A major trial this month showed for the first time that immunotherapy could work in men with advanced prostate cancer.
About one in 10 of these patients did not see their cancer grow after a year on pembrolizumab, according to research presented at the American Society of Clinical Oncology annual meeting in Chicago.
The new study, by scientists at The Institute of Cancer Research in London and University of Michigan in the US, suggests a genetic test could flag those likely to respond to the treatment.
Howard Soule, chief science officer at the Prostate Cancer Foundation, which part-funded the study, said it was a "hugely significant finding".
Researchers analysed tumour DNA from 360 men with advanced prostate cancer.
They found the tumours of seven per cent of these men were missing both copies of a gene called CDK12.
Tumours with this genetic profile contained a higher number of immune cells than other forms of prostate cancer and had a higher number of protein fragments on their surface that flag tumour cells to the immune system.
Tumours with these characteristics often respond better to immunotherapy, the researchers said, possibly because the immune system had early warning of foreign cancer cells.
Immunotherapy drugs work by stimulating the immune system to recognise and fight the cancer and are already used to treat some advanced cancers, including lung and melanoma.
