Methoxsalen with ultraviolet A therapy.

Abstract

A cohort study of 1,380 psoriasis patients treated with PUVA found that the risk of skin cancer (squamous-cell carcinoma) increased with increasing exposure to PUVA; exposure to high doses of PUVA increased the risk of cancer by more than 50-fold. The risk was independent of any possible confounding by treatment with ionizing radiation or coal tar. An association between basal-cell carcinoma and PUVA exposure also was observed; however, the estimated risk at high exposure was fourfold lower than that observed for squamous-cell carcinoma. Increased risks of skin cancer were not reported in two smaller cohort studies; one study included only 94 patients, and the other used a low dose and may not have had sufficient statistical power to detect an effect. A case-control study also reported an increased risk of skin cancer among psoriasis patients treated with PUVA. Supporting the association between skin cancer and PUVA exposure are several case reports of skin cancer (basal-cell and squamous-cell carcinoma and malignant melanoma) in patients treated with PUVA for psoriasis or mycosis fungoides. In two small randomized clinical trials evaluating whether methoxsalen would protect against sunlightinduced skin cancer (by increasing pigmentation and cornification of the skin), methoxsalen administered alone for over two years did not affect the incidence of skin cancer (IARC 1980, 1982, 1987).