Skin cancer in patients with psoriasis

BACKGROUND: Psoriasis is a chronic inflammatory skin disease that is commonly treated with ultraviolet phototherapy and systemic immunosuppressant drugs, which may confer a risk of skin cancer. Previous studies on the risk of skin cancer in patients with psoriasis have shown conflicting results. OBJECTIVES: We investigated the risk of new-onset melanoma and non-melanoma skin cancer (NMSC), respectively, in a large cohort of patients with psoriasis and psoriatic arthritis. METHODS: Data on all Danish individuals aged ≥18 years between 1 January 1997 and 31 December 2012 were linked at individual-level in nationwide registers. Incidence rates per 10 000 person-years were calculated, and incidence rate ratios (IRRs) were estimated by Poisson regression models. RESULTS: The study comprised 5 559 420 individuals with a maximum follow-up time of 16 years. There were 75 410 patients with psoriasis, and 25 087 and 58 051 individuals developed melanoma and NMSC, respectively, during follow-up. Adjusted IRRs (95% CI) of melanoma were 1.19 (1.03-1.37), 1.09 (0.75-1.58) and 1.36 (0.94-1.99), in mild psoriasis, severe psoriasis and psoriatic arthritis, respectively, and the corresponding adjusted IRRs of NMSC were 1.67 (1.55-1.81), 1.32 (1.10-1.59) and 1.62 (1.27-2.05) respectively. CONCLUSIONS: We observed a modestly increased risk of melanoma and NMSC in patients with mild psoriasis, whereas patients with severe psoriasis and psoriatic arthritis had increased risk of NMSC but not melanoma. While the risk of skin cancer is only modestly increased in patients with psoriasis, clinicians should remain vigilant.