Long-term photochemotherapy for psoriasis: a histopathological and clinical follow-up study with special emphasis on tumour incidence and behavior of pigmented lesions.

A thorough clinical and microscopical investigation was conducted in patients with severe longstanding psoriasis maintained on long-term photochemotherapy with PUVA. 250 patients were reinvestigated after PUVA therapy for up to 7 years, 49% for 5 to 7 years. No serious side effects were observed. Occasional peculiar hyperkeratoses of a bowenoid type were seen in 3 patients (1.2%) and solitary lesions at actinic keratoses in 5 patients (2%). No occurrence of squamous cell carcinoma nor basal cell carcinoma was detected. Lentiginosis of varying degree was fairly common and seen in 33% and a very profuse disseminated lentiginosis in 4%. Six patients (2.4%) developed isolated, clinically dark and irregular lentiginous spots which on biopsy showed microscopically an aberrant morphology and were therefore classified as atypical lentigines. All of them had earlier been subjected to extensive courses of UVB treatment and 3 of them had history of earlier arsenic therapy. No malignant transformation was seen but those were for reasons of safety referred to the risk group category and may prove to be at particular risk on future PUVA therapy.