A vaccine to combat prostate cancer is to be tested after studies suggested it could halve the rate of development of the disease.

Unlike the vaccines to combat the virus that causes cervical cancer, the prostate cancer vaccine is one of a number under development to make the body’s immune system attack tumors.

While the body’s immune system offers elaborate protection against invaders such as viruses and bacteria, it usually reacts only weakly to cancer because tumor cells are so similar to normal cells.

To overcome this, the company Onyvax has developed a vaccine that consists of a combination of three types of prostate cancer cell that are representative of different stages of the disease.

The cancer cells have been inactivated and cannot reproduce to create a new cancer.

The hope is that monthly injections will educate the immune system to mount an effective attack, the chief executive of Onyvax, Dr Anthony Walker, said.

Dr. Walker said this was no cure, since the tumors evolve and, under the pressure of the immune response triggered by the vaccine, develop into resistant forms. However, he believes it shows great promise in slowing the disease.

Earlier this year, Onyvax reported a trial of Onyvax-P on 28 patients by Dr. Hardev Pandha, at St. George’s Hospital Medical School, London, which showed that it may delay progression in patients who are resistant to hormone therapy.

Usually, these patients suffer a spread of the cancer to the bone about 29 weeks after the levels of a molecule used in tests for the disease, called PSA, starts to rise. Onyvax boosted this to 58 weeks, with survival even longer.