Risk of melanoma with psoralen/ultraviolet A therapy for psoriasis. Do the known risks now outweigh the benefits?

Since the introduction in the 1970s of treatment with oral psoralens with longwave ultraviolet radiation in the A range (PUVA), there has been an increasing concern about the long term carcinogenic effect of the therapy. The main indication for PUVA is psoriasis, a common, chronic and intractable skin disease that affects 1 to 3% of the world's population. The effectiveness of PUVA in inducing and maintaining the remission of severe psoriasis has been amply documented. Although psoriasis is not a life-threatening disorder, it may be associated with restriction of activities and days lost to hospitalisation. Therefore, a number of systemic treatments such as methotrexate and cyclosporin have been used. None of these treatments has been as carefully studied for long term adverse effects as PUVA. The short-term adverse effects of PUVA are generally well known and tolerated. The major mid-term adverse effect, squamous cell carcinoma of the skin, has been well documented in a number of large-scale epidemiological studies that have led to recommendations such as to restrict the lifetime number of treatments. Although squamous cell carcinoma is potentially life-threatening, it is usually slow growing and can be adequately managed by proper surveillance, treatment and follow-up. The situation is quite different for malignant melanoma, which is often fast growing and fatal. Except for anecdotal reports, malignant melanoma has not been observed in PUVA patients until recently. However, a report of a cohort of 1380 patients with psoriasis has concluded that about 15 years after the first treatment the risk of melanoma is increased approximately 5-fold in patients treated with high doses. Although this report needs to be confirmed by other multicentre trials, it is alarming since the association between exposure to ultraviolet light and development of melanoma is well established both in humans and in experimental animals. Until this study is validated, it is recommended that the guidelines for PUVA therapy should be rigorously followed and that the contra-indications should be extended to include history or family history of melanoma and patients who have already received > 200 treatments.