By the end of the year, an estimated 175,000 men in the United States will have been diagnosed with prostate cancer. Now, researchers from the UK have found a new way using immunotherapy to slow down the progression of the disease in its advanced stages, potentially adding an extra 2 years of lifespan to patients.

The immunotherapy drug, known as pembrolizumab, works by blocking the activity of a molecule called PD-1, a protein that stops cells from identifying and tackling inflamed tissues and cancer cells. By blocking this protein, the drug allows the immune system to unleash T cells that are then able to combat both inflamed tissues and cancer cells.

Already used to tackle other cancers such as melanoma, a new study by The Institute of Cancer Research, London, shows that it may be effective in treating advanced prostate cancer too. Conducted via a Phase II clinical trial, the drug was administered to 258 men with the disease who had become resistant to both androgen deprivation therapy and docetaxel chemotherapy.

In total, the researchers found that 5% of the participants saw their tumours shrink or disappear, with 19% showing other evidence of tumor response. They also saw the average survival time following treatment among a group of 166 patients with very advanced stages of the disease and high levels of prostate-specific antigen (PSA) increase to 8.1 months. Meanwhile, a second group whose PSA levels were lower, even though the disease had spread to the bone, lived for an average of 14.1 months after treatment.

In particular, the researchers found the most dramatic responses in patients whose tumors had mutations in genes that repair DNA. Known as “super-responders”, Johann de Bono, Regius Professor of cancer research at The Institute of Cancer Research, London, said, “Our study has shown that a small proportion of men with very advanced prostate cancer are super responders to immunotherapy and could live for at least two years and possibly considerably longer.”

Professor Paul Workman, chief executive of The Institute of Cancer Research, London, added, “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, the proportion of men are responding well to treatment….'It's encouraging to see testing for DNA repair mutations may identify some patients who are more likely to respond, and I'm keen to see how the new, larger trial in this group of patients plays out.”



Sources: Melanoma Research Alliance, Daily Mail and BBC News