Abstract
Skin cancer is most frequently diagnosed in the White population. However, its subtypes and epidemiology in Japan are understudied. We aimed to elucidate skin cancer incidence in Japan based on the National Cancer Registry, a new nationwide integrated population-based registry. Data from patients diagnosed with skin cancer in 2016 and 2017 were extracted and classified by cancer subtypes. Data were analyzed using the World Health Organization and General Rules tumor classifications. Tumor incidence was calculated as the number of new cases divided by the corresponding total person-years. Overall, 67,867 patients with skin cancer were included. The percentage of each subtype was as follows: basal cell carcinoma, 37.2%; squamous cell carcinoma, 43.9% (18.3% of which, in situ); malignant melanoma, 7.2% (22.1% of which, in situ); extramammary Paget's disease, 3.1% (24.9% of which, in situ); adnexal carcinoma, 2.9%; dermatofibrosarcoma protuberans, 0.9%; Merkel cell carcinoma, 0.6%; angiosarcoma, 0.5%; and hematologic malignancies, 3.8%. The overall age-adjusted incidence of skin cancer was 27.89 for the Japanese population model and 9.28 for the World Health Organization (WHO) model. The incidences of basal cell carcinoma and squamous cell carcinoma were the highest (3.63 and 3.40 per 100,000 persons, respectively, in the WHO model) among skin cancers, whereas the incidences of angiosarcoma and Merkel cell carcinoma were the lowest (0.026 and 0.038 per 100,000 persons, respectively, in the WHO model). This is the first report to provide comprehensive information on the epidemiological status of skin cancers in Japan using population-based NCR data.