Psoriasis balm boosts melanoma risk.

Most people grow a new skin every 30 days. People with psoriasis, however, grow new layers of skin much more rapidly. In this condition, the new skin is inflamed and abnormal, marred by clumps of immature cells that form red, scaly lesions.

One of the few effective, well-tolerated remedies for severe psoriasis is a plant derivative called psoralen, which slows skin growth when combined with exposure to ultraviolet A light. Several studies have associated long-term use of the therapy--known as PUVA--with squamous cell carcinoma, a usually treatable form of skin cancer.

Now, researchers have also linked PUVA to malignant melanoma, perhaps the deadliest of all skin cancers. The evidence arose in a study of 1,380 people treated regularly with PUVA since 1975, report Robert S. Stern of Harvard Medical School in Boston and his colleagues.

Between the start of PUVA therapy and 1990, these people developed only four melanoma tumors, about the number that might be expected in the overall population. Over the next eleven years, however, seven of them developed eight melanomas. Three of the people have died of melanoma, according to a report in the April 10 New England Journal of Medicine.

On the basis of this and other findings, the researchers calculate that the risk of melanoma rises after 15 years, especially in people who have received 250 or more doses of PUVA. People who receive these treatments often "should be followed carefully" so cancers can be detected and treated early enough to save lives, Stern and his colleagues advise.

Klaus Wolff of the University of Vienna asserts that "we cannot now afford to abandon PUVA," despite the melanoma risk, because "PUVA offers innumerable patients the chance to resume a normal life." Wolff echoes Stern in an editorial asserting that doctors should adhere to treatment guidelines and observe patients for cancer.