Psoriasis and risk of 26 cancers: pooled population-based cohort studies from Denmark, England, Israel and Taiwan

BACKGROUND: Psoriasis is a chronic inflammatory skin disease, and the risk of developing cancer has been postulated due to the presence of several plausible underlying mechanisms. Understanding the association between psoriasis and cancer is imperative to the provision of optimal psoriasis care. OBJECTIVES: To examine the risk of developing cancer in individuals with psoriasis. METHODS: Population-based cohort studies were conducted in Denmark, England, Israel and Taiwan through the use of linked electronic health records. Individuals aged at least 18 years with a diagnosis of psoriasis in the country-specific study period were matched with up to six comparators with no record of psoriasis prior to the index date. Country-specific hazard ratios for the risk of cancer development overall and for 26 site-specific cancers between individuals with and without psoriasis were calculated through Cox regression. Country-specific estimates were pooled using random effects modelling. RESULTS: We included 702 022 individuals with psoriasis and 4 185 342 matched comparators. In models implicitly controlled for age, sex and calendar time by matching, there was a small association between psoriasis and cancer overall [pooled HR (pHR) 1.08, 95% confidence interval (CI) 1.04-1.13; I2 = 92.4%]. Adjustment for potential confounding factors resulted in a slight attenuation of risk (pHR 1.05, 95% CI 1.01-1.09; I2 = 81.2%). When restricted to those with moderate-to-severe psoriasis, the risk of cancer overall was slightly higher (pHR 1.16, 95% CI 1.04-1.28; I2 = 92.8%) than in confounder-adjusted models (pHR 1.09, 95% CI 1.03-1.15; I2 = 60.6%). Associations with psoriasis were present for oral cavity (pHR 1.29, 95% CI 1.12-1.47; I2 = 55.4%), pharynx (pHR 1.30, 95% CI 1.07-1.58; I2 = 58.4%), oesophagus (pHR 1.17, 95% CI 1.03-1.33; I2 = 56.6%), liver (pHR 1.53, 95% CI 1.33-1.77; I2 = 75.1%), pancreas (pHR 1.09, 95% CI 1.02-1.17; I2 = 0.0%), kidney (pHR 1.19, 95% CI 1.11-1.27; I2 = 0.0%), bladder (pHR 1.13, 95% CI 1.06-1.20; I2 = 28.7%) and keratinocyte cancers (pHR 1.37, 95% CI 1.16-1.63; I2 = 97.5%), and Hodgkin lymphoma (pHR 1.56, 95% CI 1.16-2.11; I2 = 69.7%), non-Hodgkin lymphoma (pHR 1.16, 95% CI 1.07-1.26; I2 = 35.5%) and leukaemia (pHR 1.18, 95% CI 1.08-1.29; I2 = 41.9%). Site-specific associations generally persisted, with slight risk exacerbations and additional associations for lung and ovarian cancers, when limited to people with moderate-to-severe psoriasis. CONCLUSIONS: Psoriasis was associated with an increased risk of developing 14 of 26 investigated site-specific cancers, including cancers with a poor prognosis, such as liver, lung and oesophageal cancer. Our findings can be used to reinforce cancer prevention strategies in psoriasis care.