Skin carcinoma in patients with psoriasis treated with topical tar and artificial ultraviolet radiation.

A case-control study, consisting of 59 skin cancer patients with severe psoriasis, was conducted to evaluate the effect of treatment with tar and/or artificial ultraviolet radiation on the risk of developing cutaneous carcinoma. Using 924 unmatched controls, we estimated that the crude rate of skin cancer was 2.4-fold for patients with high exposure to tar and ultraviolet radiation, compared with those lacking high exposure. Using a control series of 126 patients matched for age, skin type, region of residence, sex, history of exposure to ionising radiation, and number of 8-methoxypsoralen photochemotherapy treatments, we observed a stronger association (relative rate = 4.7, 95% confidence limits = 2.2 to 10.0). The magnitude of the relative rates argues for continued surveillance for tumours among patients with psoriasis who receive long-term tar or artificial ultraviolet radiation therapy.