No abstract

This study was designed to estimate the relative cancer risk of patients with moderate to severe psoriasis, with reference to different treatments. A cohort of 5687 hospitalized patients with psoriasis obtained from the Finnish Hospital Discharge Register in 1973-84 was linked with the records of the Finnish Cancer Registry. Standardized incidence ratios for cancer were calculated by dividing the observed number of cases by the expected cases, which were based on the national sex-specific and age-specific cancer incidence rates. By the end of 1995, 533 cancer cases were observed in the cohort. The overall cancer incidence was increased (standardized incidence ratio 1.3, 95% confidence interval 1.2-1.4). The estimated relative risks were highest for Hodgkin's disease (standardized incidence ratio 3.3, 95% confidence interval 1.4-6.4), squamous cell skin carcinoma (standardized incidence ratio 3.2, 95% confidence interval 2.3-4.4), non-Hodgkin's lymphoma (standardized incidence ratio 2.2, 95% confidence interval 1.4-3.4), and laryngeal cancer (standardized incidence ratio 2.9, 95% confidence interval 1.5-5.0). The role of prior oral antipsoriatic medications or phototherapy on the development of these cancers was assessed in a nested case-control study, for which 67 cases and 199 sex and age matched controls were selected from the psoriasis cohort. The relative risks were estimated using conditional logistic regression analysis. Oral 8-methoxy-psoralen plus ultraviolet-A radiation therapy and the use of retinoids were associated with an increased risk of squamous cell skin carcinoma (relative risk adjusted for the other treatment variables 6.5, 95% confidence interval 1.4-31, and 7.4, 95% confidence interval 1.4-40, respectively), whereas none of the treatments could be linked with the occurrence of non-Hodgkin's lymphoma.

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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.

No abstract