Carcinogenic risk of bath PUVA in comparison to oral PUVA therapy

The potential carcinogenic risk of bath PUVA therapy was compared to that o f systemic (oral) PUVA. An analysis of the epidemiological data on cancer r isk following bath PUVA with trimethylpsoralen does not support the conclus ion that bath PUVA per se is less carcinogenic than systemic PUVA with 8-me thoxypsoralen (8-MOP). Pharmacokinetic studies indicate that both the conce ntration of 8-MOP in the target organ for PUVA carcinogenicity (skin) at th e relevant time point (time point of UVA irradiation) and the extents of bi ological effects in the skin are comparable following bathwater or systemic 8-MOP administration, Furthermore, the therapeutic effects of PUVA arise f rom the same photochemical reaction mechanisms as do the carcinogenic effec ts. Theoretically, the ratio of (desired) cytotoxic versus (undesired) muta genic effects could increase with increasing efficiency of the PUVA therapy itself, On the basis of the available evidence, it is concluded that all f orms of PUVA therapy, independently of the route of 8-MOP administration, c ontribute to a smalt but dose-dependent increase in nonmelanoma skin cancer risk.