History of chronic inflammatory disorders increases the risk of Merkel cell carcinoma, but does not correlate with Merkel cell polyomavirus infection

Background: We aimed to assess the connection between chronic inflammatory disorders (CIDs) and Merkel cell carcinoma (MCC). Methods: Merkel cell carcinoma cases diagnosed in 1978–2009 were extracted from the Finnish Cancer Registry and controls from the Population Registry. Information on reimbursed CIDs was linked to clinicopathological data including Merkel cell polyomavirus (MCV) status by qPCR and immunohistochemistry for the large T antigen of MCV (LTA), Ki-67 and tumour-infiltrating lymphocytes. Results: Chronic inflammatory disorders increased the risk of MCC significantly (odds ratio (OR) 1.39, 95% confidence interval (CI) 1.03–1.88), specifically connective tissue/systemic diseases (OR 1.75, 95% CI 1.09–1.80) and diabetic conditions (OR 1.51, 95% CI 1.03–2.22). Chronic inflammatory disorders associated with larger tumour diameter ( P =0.02) and higher Ki-67 expression ( P =0.005). The expression of LTA was seen significantly more often in the absence of CIDs ( P =0.05). Conclusions: Patients with CID are at significantly higher risk for aggressive MCC. Merkel cell polyomavirus positivity is more common in MCC patients unafflicted by CID.