A major clinical study has demonstrated that immunotherapy pembrolizumab can extend life expectancy in men with advanced prostate cancer.
The Phase II clinical study conducted by a team at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust showed that one in 20 men with end-stage prostate cancer responded to pembrolizumab.
Researchers found that a small proportion of men were ‘super responders’ and were still alive after the trial had concluded.
The trial was funded by drug manufacturer Merck and included 258 men with advanced prostate cancer who had previously been treated with and become resistant to androgen deprivation therapy and docetaxel chemotherapy.
Results showed that around 5% of men treated with pembrolizumab saw their tumours shrink or disappear, and almost 19% had some evidence of tumour response with a decrease in prostate-specific antigen (PSA) level.
The average length of survival was 8.1 months with pembrolizumab among a group of 166 patients with specifically advanced disease and high levels of PSA.
The disease disappeared or partly disappeared on scans in nine patients, with four ‘super-responders’ remaining on treatment at the end of study follow-up. Responses lasted for up to 22 months.
Results also revealed that the second group of patients, whose PSA levels were lower but whose disease had spread to the bone, lived for an average of 14.1 months on pembrolizumab.
The Phase II clinical trial also compared the efficacy of pembrolizumab in men whose tumours had a protein known as PD-L1 on the surface of their cancer cells, as well as those whose tumours did not.
Data also showed that testing for PD-L1 was not sufficient to know which patients would respond to treatment. Men with PD-L1 in their tumours survived 9.5 months compared to 7.9 months for patients without PD-L1 in their tumours.
The Institute of Cancer Research chief executive Professor Paul Workman said: “Immunotherapy has had tremendous benefits for some cancer patients and it’s fantastic news that even in prostate cancer, where we don’t see much immune activity, a proportion of men are responding well to treatment.”