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Immune system turned against prostate cancer

Published Oct. 1, 2005

An experimental vaccine that revs up the body's natural defenses is showing early promise in victims of advanced prostate cancer.

Prostate cancer kills 42,000 Americans annually, making it the second leading cancer killer among men, and it is one of the most difficult of all tumors to treat once it has spread. Ordinary chemotherapy drugs are virtually useless.

Now, doctors are trying to use the body's own cancer surveillance system to track down malignant prostate cells that have escaped throughout the body.

They call their strategy a vaccine. However, unlike ordinary vaccines that keep people from catching diseases, this one is intended to fight an established illness.

Dr. Gerald P. Murphy of the Pacific Northwest Cancer Foundation in Seattle described his research Wednesday at a conference sponsored by the American Cancer Society.

Prostate cancer cells that are spreading through the body carry a protein called prostate-specific membrane antigen. Normally, the presence of the antigen should fire up the immune system to hunt down cancer cells and kill them.

Unfortunately, the body often fails to send out a warning to look for cells carrying this antigen. So the cancer grows unchecked.

Murphy's idea is to fire up the cells that give this warning.

Researchers tested the treatment on 51 men with advanced prostate cancer who had failed to respond to all other therapy. Although the experiment was intended largely to show the safety of the procedure, seven men improved.

"We were quite surprised to see these responses," Murphy said. "They have lasted from 125 days up to 300 days-plus."

Among them was one man with extensive cancer in his bones. Since the treatment, his PSA level _ the main test for prostate cancer _ has fallen to undetectable amounts. His pain has stopped, he has gained weight and his bone scans look normal.

In the next phase of the study, the researchers are treating 64 more patients, half with widespread disease and half with cancer in the early stages of spreading.

Dr. Donald Coffey of Johns Hopkins Hospital called Murphy's work "a hallmark discovery."