For many years, physicians believed that the immune system was effective only in combating infectious diseases caused by such invading agents as bacteria and viruses. More recently, we have learned that the immune system may play a central role in protecting the body against cancer and combating cancer that has already developed.

This latter role is not well understood, but there is evidence that in many cancer patients the immune system slows down the growth and spread of tumors. The body's ability to develop an immune reaction to tumors may help determine which patients are cured of cancer using conventional therapies, including surgery, radiation and drugs.

Immunotherapy appeared to have had benefic results in the case of a 52-year-old man from Oregon, diagnosed with melanoma that had spread to a lung and to a lymph node in his groin and had not responded to other therapies. His disease went into complete remission.

Melanoma is the most serious form of skin cancer and is due mostly to excessive sun exposure, which causes mutation. The disease starts with a tiny mole, which begins growing relentlessly within a couple of months, spreading cancer cells throughout the body. About 62,000 cases are diagnosed in the U.S. yearly and one American dies from this disease every hour, statistics of the American Cancer Society show. If caught on time, melanomas can be easily treated by surgically removing the cancerous patch of skin, while nothing can be done once it spreads to other parts of the body.

Dr. Cassian Yee, an associate member at Fred Hutchinson’s Cancer Research Center in Seattle and author of a study appeared in the June 19 edition of the New England Journal of Medicine said the man enrolled on July 2005 in a clinical trial along with eight other people.

Scientists at Fred Hutchinson concentrated on a type of white blood cell called a CD4+T cell. Previously, scientists had difficulty isolating and copying immune system cells, according to the report. They could select these cells from a sample of the man’s white blood cells and made five billion copies, which were all put back to see whether they could mount an effective attack on the tumors.

Surprisingly, after two months, scans showed the tumors were completely gone and after two years, the man remained disease-free. According to Dr. Yee, the injected T cells remained active in the patient’s body for at least 80 days. However, after two years, the researchers fell out of contact with the man and his current condition is not known.

The eight other patients enrolled in the trial were also given the treatment, which stopped the disease from spreading in some of them, but it is too early to tell if any will respond as well as the man whose cancer was cured, Dr. Yee said.

However efficient immunotherapy was in the Oregon man’s case, Dr. Yee said “we need to confirm the effectiveness of therapy in a larger study.”

The therapy is far from becoming a standard one, but, if proven successful in more patients, Dr. Yee predicted the therapy could be used for the 25 percent of all late-stage melanoma patients who have the same immune-system type.