Psoriasis, its treatment, and cancer in a cohort of Finnish patients.

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.