Doctors say they successfully treated an Oregon man fighting a deadly skin cancer with an experimental treatment that they say may have revved up his immune system to fight the tumours.

The man, 52, went into remission after being told he had less than a year to live, according to a report in Thursday's issue of the New England Journal of Medicine.

The patient's dramatic turnaround was the only success in a small study, leading doctors at the Fred Hutchinson Cancer Research Center in Seattle to be cautious in their enthusiasm.

They said the man's tumours had disappeared two months after the treatment and he reported no symptoms of the disease two years after he was treated in July 2005, but researchers are not aware of his current condition.

Still, the researchers are counting the single case out of nine in the experiment as the latest in a small series of successes involving immune-priming treatments against deadly skin cancers.

Dr. Steven Rosenberg of the National Cancer Institute, a pioneer in this field of research, said the idea of immune system cells latching on to and attacking skin cancers is not a new one.

Killer cells cultivated in laboratory

In recent experiments, Rosenberg and other researchers have focused on ramping up a certain kind of immune system cell — the "killer T cells" that envelop and kill foreign agents.

The Hutchinson Center scientists focused on specific helper T cells that are adept at locking onto a cancer cell and guiding the killer cells to their target.

The researchers drew blood from patients, located the special helper cells and then grew more of them in the laboratory. They then put roughly five billion of the cells back into the patients, without chemotherapy or the other harsh drugs.

It's possible the treatment spurred the man's immune system to expand its cancer-fighting ability in new ways, said study co-author Dr. Cassian Yee.

However, the case raised many unanswered questions. The man had been treated earlier with other drugs. Researchers think it's possible those treatments had already weakened or altered the cancer.

The Canadian Cancer Society estimates 4,600 Canadians developed melanoma in 2007.

The biggest contributing factor in the development of melanoma is the skin's sensitivity to ultraviolet (UV) rays. Melanoma cancers typically start in areas exposed only occasionally to the sun, such as the back and the backs of the legs.

With files from the Associated Press