[Reevaluation of precancerous lesions of the skin]

Precancerous skin lesions are categorized into three groups; (1) carcinoma in situ, (2) hereditary precancerous lesions, and (3) non-hereditary precancerous lesions. Carcinoma in situ includes Bowen's disease, actinic keratosis and leukoplakia as squamous cell carcinoma in situ, Paget's disease as adenocarcinoma in situ, and melanoma in situ. Hereditary precancerous lesions include xeroderma pigmentosum, epidermodysplasia verruciformis and porokeratosis. The mechanisms of carcinogenesis in these diseases are investigated intensively. Chronic radiodermatitis and other scars are treated as non-hereditary precancerous lesions.