Incidence and geographic differences in keratinocyte carcinoma and Bowen's disease in office‐based dermatological practice between 2013 and 2022: A nationwide Danish registry‐based study

Abstract Background Rates of keratinocyte carcinoma (KC) across Europe are impacted by population demographics and geography. Regional differences in KC occurrence exist, but few European studies investigate incidences of specific subtypes in the secondary healthcare sector on a national level. Objectives To determine geographical differences in incidence rate and lifetime risk of KC subtypes across Denmark, including nodular and superficial basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and the KC precursor, Bowen's disease (BD), identified in office‐based dermatological practice. Methods Based on a nationwide registry (The Danish Skin Cancer Registry), all patients in Denmark's five regions with a histologically‐ or clinically verified KC or BD registered in a state‐funded office‐based dermatology practice between 2013 and 2022 were included. Trends in national‐ and region‐specific age and sex standardised tumour incidence rates (STIR) were calculated. Further, national lifetime risk of each tumour subtype was estimated. Results Between 2013 and 2022, the combined STIR for KC/BD rose 172% nationally from 180 to 489 per 100,000 person‐years (PY). This increase reflected rising rates of nodular BCC, SCC, and BD, while superficial BCC incidence was relatively stable. Regional differences in STIR for combined KC/BD were observed, with the Capital Region and North Jutland generally demonstrating higher rates than Zealand, Southern‐ and Central Denmark (e.g., North Jutland vs. Southern Denmark: 714 vs. 405/100,000PY). While the estimated lifetime risk of developing at least one KC or BD tumour was 21.8%, risk varied with tumour subtype, resulting in subtype‐specific risks of 16.4%, 5.1%, 1.9% and 1.3% for nodular BCC, superficial BCC, SCC, and BD, respectively. Conclusions In Denmark's secondary dermatological care sector, incidence of nodular BCC, SCC and BD continues to rise with an overall lifetime risk nearing 22%. While KC incidence is increasing in Denmark, the study detected differences in geographical trends and rate increases of specific tumour subtypes.