Trioxsalen bath PUVA did not increase the risk of squamous cell skin carcinoma and cutaneous malignant melanoma in a joint analysis of 944 Swedish and Finnish patients with psoriasis.

It has been suggested that trioxsalen bath and ultraviolet (UV) A (PUVA) is associated with a very low or no risk of non-melanoma skin cancer, but the numbers of patients in individual studies have been limited. In order to attain statistically relevant information about the cancer risk associated with trioxsalen bath PUVA, two follow-up studies were combined and the joined cancer incidence was analysed among 944 Swedish and Finnish patients with psoriasis. The mean follow-up time for skin cancer was 14.7 years. Standardized incidence ratios (SIR) were calculated as a ratio of observed and expected numbers of cases. The expected numbers of cases were based on the national cancer incidence rates in the respective countries. There was no excess of squamous cell skin carcinoma [SIR 1.1, 95% confidence interval (CI) 0.2-3.2] or malignant melanoma (SIR 0.9, 95% CI 0.1-3.2) in the combined cohort. Basal cell skin carcinoma was not studied. The incidence of all non-cutaneous cancers was not increased (SIR 1.1, 95% CI 0.8-1.4). A threefold excess risk of squamous cell skin carcinoma after trioxsalen bath PUVA could therefore be excluded, which is a markedly lower risk than that associated with oral 8-methoxypsoralen PUVA. The result needs to be confirmed in a future follow-up, however, as the number of patients with high PUVA exposures was low.