RESUMO
Background: 8‑oxoguanine, a major product of DNA oxidation, is considered a key parameter in measuring the carcinogenic effects of ultraviolet radiation. Objective: To assess and compare the carcinogenic potential of different photo (chemo) therapeutic modalities in photoresponsive skin diseases by measuring the levels of 8‑oxoguanine in dark‑skinned individuals before and after photo (chemo) therapy. Methods: A prospective, randomized controlled pilot study was conducted in 63 patients of skin types III–V with photo‑responsive dermatoses including vitiligo, psoriasis and mycosis fungoides. Patients were divided into three groups; Group 1 (received narrowband ultraviolet‑B), Group 2 (received psoralen plus ultraviolet‑A) and Group 3 (received broadband ultraviolet‑A). Biopsies were taken before and after phototherapy to measure 8‑oxoguanine levels using enzyme‑linked immunosorbent assay. Biopsies were also taken from the sun‑protected skin in 21 controls subjects who had no dermatological disease. Results: Regardless of the disease, a significantly higher level of 8‑oxoguanine was found after treatment when compared to the pre‑treatment baseline levels; however, these levels were comparable to those in control subjects. A weakly significant positive correlation was found between cumulative dose and 8‑oxoguanine levels following psoralen plus ultraviolet‑A therapy. In controls, comparing the 8‑oxoguanine levels between skin types III and IV showed significantly lower 8‑oxoguanine in skin type IV. Conclusion: Therapeutic doses of ultraviolet radiation are relatively safe in dark skinned patients; however, minimizing the cumulative dose of phototherapeutic modalities (particularly psoralen plus ultraviolet‑A) is recommended.