LONDON, Nov 28: A drug which makes a wide range of cancers more vulnerable to the body's immune system is "exciting" and may mark a new era, say doctors.
It strips cancer cells of the "camouflage" they use to evade attack by the immune system.
In the most detailed study, published in Nature, some patients completely recovered from terminal bladder cancer.
Cancer Research UK said the field of immunotherapy was delivering "a lot of very exciting results".
The immune system is in delicate balance with some chemicals in the body encouraging a strong vigorous response, while others try to dampen it down.
Tumours can hijack this system to hide from the immune system.
One trick which tumours use is a protein called PD-L1 which is normally used to prevent autoimmune diseases.
An international team of scientists has been trialling a drug to block PD-L1, produced by the company Roche, on 68 people with advanced bladder cancer.
All the patients had tried chemotherapy and had been given six-to-eight months to live.
More than half the patients, whose tumours were using PD-L1 to hide from the immune system, showed signs of recovery.
In two patients there were no signs of cancer after the treatment.
One in ten patients responded to the experimental therapy even if PD-L1 was not present in the tumour.
Dr Tom Powles, an oncologist at the Barts Cancer Institute at Queen Mary University of London and part of the research team, said "There have been no new drugs for bladder cancer for 30 years. ?BBC Online