Risk and predictors of psoriasis in patients with breast cancer: a Swedish population-based cohort study

BACKGROUND: The risk of psoriasis in patients with breast cancer is largely unknown, as available evidence is limited to case findings. We systematically examined the incidence and risk factors of psoriasis in patients with breast cancer. METHODS: A Swedish nationwide cohort of 56,235 breast cancer patients (2001–2012) was compared to 280,854 matched reference individuals from the general population to estimate the incidence and hazard ratio (HR) of new-onset psoriasis. We also calculated HRs for psoriasis according to treatment, genetic, and lifestyle factors in a regional cohort of 8987 patients. RESULTS: In the nationwide cohort, 599 patients with breast cancer were diagnosed with psoriasis during a median follow-up of 5.1 years compared to 2795 cases in the matched reference individuals. This corresponded to an incidence rate of 1.9/1000 person-years in breast cancer patients vs. 1.7/1000 person-years in matched reference individuals. Breast cancer patients were at an increased risk of psoriasis (HR = 1.17; 95% confidence interval (CI) = 1.07–1.28), especially its most common subtype (psoriasis vulgaris; HR = 1.33; 95% CI = 1.17–1.52). The risk of psoriasis vulgaris was highest shortly after diagnosis but remained increased up to 12 years. Treatment-specific analyses indicated a higher risk of psoriasis in patients treated with radiotherapy (HR = 2.44; 95% CI = 1.44–4.12) and mastectomy (HR = 1.54, 95% CI = 1.03–2.31). Apart from treatment-specific effects, we identified genetic predisposition, obesity, and smoking as independent risk factors for psoriasis in breast cancer patients. CONCLUSIONS: The incidence of psoriasis is slightly elevated among patients with breast cancer, with treatment, lifestyle, and genetic factors defining the individual risk profile. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12916-017-0915-4) contains supplementary material, which is available to authorized users.