Supplementary Material for: Prevalence of Actinic Keratosis in Patients Attending General Practitioners in Switzerland

Background: Most of the data concerning the prevalence of actinic keratosis (AK) originate from the USA and Australia, and recently from Austria and Spain, but are based on populations in dermatology practices. Switzerland is the leading country with skin cancer incidence in Europe. AK prevalence among the Swiss population is therefore an important public health issue. Objective: To assess the prevalence of AK in the outpatient Swiss population in general practice. Methods: General practitioners captured AK diagnosis stage and localization in consecutive patients, who attended the physician for any reason. Results: A total of 2,844 consecutive patients (55.7% female) were enrolled in 59 general practitioners’ offices. AK prevalence was 25.3% and increased steadily with age; 33% of men and 19% of women were diagnosed with AK. Every second AK patient declared leisure-related UV exposure, while only 23% were exposed to UV occupationally; 16% of the patients were UV exposed both occupationally and during leisure. AK distribution among sun-exposed body sites and extent of disease varied by sex. Conclusion: In Switzerland AK is a common diagnosis in dermatology practices. Since up to 5% of AK may progress to invasive squamous cell carcinoma (SCC), prevention of AK, as well as education of patients and general practitioners, may play a critical role for subsequent SCC development. This is the first study on AK prevalence in Switzerland identifying patients most affected by AK. These results will help to define future approaches to target general practitioners for education, screening, and specific intervention in patients with AK.