Double trouble: risks of psoriasis therapy.

Double trouble: Risks of psoriasis therapy

A widely used treatment for severe psoriasis, a chronic skin condition, carries long-term risk of several cancers, according to two reports in THE JOURNAL OF INVESTIGATIVE DERMATOLOGY.

A study of 1,380 patients at 16 U.S. medical centers now shows that high-dose treatment with a photosensitizing drug and ultraviolet light, an approach known as PUVA, increases the risk of two usually nonfatal skin cancers, according to a report in the journal's August issue. PUVA combines the effect of the drug psoralen with exposure to ultraviolet light in the A range (UVA) to retard the speeded-up maturation and shedding of skin cells characteristic of psoriasis.

"The important finding is that these patients continue to develop squamous cell carcinoma [five years after initial treatment] at a rate far higher than that seen in the general population," says Robert S. stern, of Harvard Medical School in Boston, who led the research. The report of the Photochemotherapy Follow-Up Study confirms and extends the group's previous finding that after two years of treatment PUVA "could promote" the development of this skin cancer.

The risk for squamous cell cancer in high-dosage patients -- about 60 times higher than for the general population -- increased with dosage, the research group found, with the risk 12 times greater for those who received over 260 PUVA treatments than for those who received 160 or fewer treatments. In addition, the researchers noted a "modest" increase in risk for basal cell carcinoma, also dose related. More than 500,000 new cases of the two skin cancers occur annually in the United States.

PUVA is "clearly only for people with severe psoriasis," Stern concludes. He notes the trend is to reduce PUVA exposure by alternating it with other treatments, and that patients may have to accept less-than-complete clearing of their skin. Severe psoriasis, with red, scaly patches over more than 30 percent of the body, can cause dry, cracked skin, intense itching and swelling that interferes with movement.

In the second report, in the September issue, the research group reports that while the overall incidence of death and causes of death are "comparable" in the study group to rates in the general population, several concerns emerge that warrant further investigation. Seven PUVA-treated patients in the study developed primary central nervous system tumors, which is five times more than expected, and represents a "significant" number, according to Stern. (Six of the seven developed glioblastoma in the brain; one developed melanoma of the eye.) Whether this increase relates to PUVA or to other treatments many patients use for psoriasis, including tar shampoos and topical tar, remains unclear, Stern says. "And there was nothing to indicate any association between PUVA dosage and these tumors."

Although PUVA treatment can suppress the immune system, the incidence of other cancers that might be expected to develop in treated patients -- melanoma, leukemias and lymphomas -- does not appear to increase. But further follow-up will be necessary to eliminate the possibility of risk for such long-latency cancers, the researchers say. "For the most part, the news is reassuring," says stern. "PUVA is quite an effective therapy that should be used judiciously."