Carcinogenic risk of psoralen plus ultraviolet radiation therapy: evidence in humans.

Despite differences in study populations, methodologies, and levels of psoralen plus UV irradiation at 320-400 nm (PUVA), results from 4 prospective studies of patients treated with PUVA support the hypothesis that the risk of squamous cell carcinoma is increased with prolonged exposure. Tumors that develop after PUVA exposure behaved like skin tumors associated with sun exposure. In view of the latency for cancer in humans, continued prospective follow-up is required if we are to determine the ultimate carcinogenic risk of this type of therapy.