A study conducted by doctors at the Medical School concludes that a new psoriasis treatment. known as photochemotherapy (PUVA), increases the risk of two types of skin tumors in certain high-risk patients.

The report, published in the New England Journal of Medicine, indicates that most patients face no additional risk from the new technique, which uses a combination of ultraviolet light and special drugs.

Photochemotherapy was first introduced in 1974, when dermatologists hailed it as a major advance in the treatment of psoriasis. It is still in the testing stage, although almost 35,000 people received the treatment last year.

"The study pinpoints who should and who should not receive PUVA treatment," Robert S. Stern, instructor in Dermatology at the Medical School, said yesterday. We've shown that people with previous X-ray skin treatment or who have had skin tumors in the past are at a higher risk with the photochemotherapy treatment," Stern said.

"For people without these risk factors, PUVA is a great way to clear up the disease," Stern added.

He said the cancer present in patients with the risk factors is not life-threatening. "The cancers observed are relatively minor, local tumors that can be excised in the office of the patient's doctor," he said. "The lesions cause no pain," he added.

Treatment of Choice

The study concluded that photochemotherapy is so highly effective that it should remain as the treatment of choice for many severe psoriasis problems that resist conventional therapy, Dr. John A. Parrish, associate professor of Dermatology at the Medical School, said yesterday.

"An American moving to Australia and becoming a fisherman is as likely to develop cancer as a psoriasis patient without risk factors receiving photochemotherapy," Parrish added.

The study was conducted at Beth Israel Hospital and Massachusetts General Hospital, two of Harvard's teaching hospitals.