Incidence and outcomes of Merkel cell carcinoma related to Merkel cell polyomavirus status in Iceland in 1981-2023

Background: Impact of Merkel cell polyomavirus (MCPyV) associated Merkel cell carcinoma (MCC) has not been assessed in the Icelandic population, nor in a whole population elsewhere. Objectives: The primary objective was to assess trends in the incidence of MCC in Iceland and the association with MCPyV. Secondary objectives aimed to analyze MCC outcomes. Methods: In this retrospective cohort study, patients diagnosed with MCC between 1981 and 2021 were identified from the Icelandic Cancer Registry. Patients were separated into 2 groups based on MCPyV immunochemistry staining. Age-standardized incidence was calculated and Joinpoint analysis was used to assess incidence trends. A Cox proportional hazards model was used to assess survival differences between the 2 groups. Results: Overall incidence of MCC increased from 0.015 to 0.26 per 100,000 persons, though the incidence of MCPyV positive cases recently decreased while negative cases increased. MCPyV negative tumors were associated with sun exposure (P < .01), a history of keratinocyte carcinoma, smaller tumor size, and lower overall survival. Limitations: Even with population-level data, comprehensively investigating associations with MCC is difficult due to its rarity. Conclusion: MCPyV negative MCC tumors were associated with lower survival despite smaller tumor size. Thus, MCPyV status could be an important prognostic biomarker.