Background: Chronic inflammatory conditions such as psoriasis may pose an increased risk of cancer due to impaired immunosurveillance resulting from the chronic inflammation and immunosuppressive medications. However, the relationship between psoriasis and the risk of melanoma is still controversial. Objective: To compare the occurrence of melanoma in a cohort of 72,739 psoriasis patients and in 25,956 non-dermatological patients. Methods: A record-linkage was performed between records of hospitalizations and access to day-hospital and day-surgery clinics and outpatient clinics. The frequency of melanoma was compared between psoriasis patients and vascular surgery patients. Occurrence of melanoma was compared by computing the relative risk (RR) and modelled using multiple logistic regression. Results: Overall, occurrence of melanoma was 1.8% (95% CI 1.5-2.2%) in psoriasis patients and 4.5% (95% CI 3.8-5.4%) in non-dermatological patients (RR = 0.40, 95% CI 0.31-0.51). The simultaneous adjustment for gender, age, and phototherapy yielded a RRadj = 0.54(95% CI 0.41-0.70. For patients who underwent phototherapy, vs. those who did not, the RRadj was 1.50 (95% CI 0.56-4.15). Conclusions: In this large retrospective study, patients with psoriasis had a significantly lower probability of having melanoma when compared to a group of non-dermatological patients. Further studies, preferably with a concurrent longitudinal design to estimate incidence with more complete information, are needed to corroborate our findings.
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