[Reasons for the increased incidence of skin cancer].

The cutaneous malignancies with an increasing incidence in Japan are squamous cell carcinoma, basal cell carcinoma, and malignant melanoma. As a precancerous state or early lesion, actinic keratoses also deserve attention. According to a nationwide questionnaire survey (responses from 94 centers), basal cell carcinoma has the highest incidence and accounts for nearly 50% of all skin malignancies, followed by squamous cell carcinoma (31%) and malignant melanoma (21%). The number of cases of each tumor has grown annually, and comparison of the percent increases between 1987 and 2001 shows an increase of about 1.5-fold for basal cell carcinoma or 1.7-fold for squamous cell carcinoma or malignant melanoma. Supported by a Grant-in-Aid for Cancer Research from the Ministry of Health, Labor and Welfare, the Malignant Skin Tumor Research Group has been investigating the factors behind these increases by detailed statistical analysis of data obtained from 1987 onwards from designated centers (19-22 centers). Numerous factors have been suggested by this research, but the most important was concluded to be ultraviolet radiation.