[Precancerous tumors and carcinomas in situ of the skin].

Precancerous skin lesions and carcinomas in situ of the skin represent the early stages of epithelial skin tumors. There is no invasive tumor growth, so the basement membrane is completely intact. These lesions show a wide variation of clinical and histological appearances on the skin or mucosa. The precancerous and carcinoma in situ lesions that are described in this text are actinic keratosis, actinic cheilitis, cutaneous horns, arsenical keratosis, tar-induced dermatosis, X-ray irradiation-related keratosis, Bowen's disease, erythroplasia of Queyrat, bowenoid papulosis, intraepithelial neoplasia (vulvar, penile and anal). Because they all can progress into invasive carcinoma, therapy is mandatory. Many noninvasive therapeutic approaches exist nowadays in the form of gels, creams, photodynamic therapy and invasive techniques such as laser therapy and cryotherapy, curettage and excision of lesional skin. Depending on the treatment process, different rates of general clearance and recurrence of the lesions are discussed in this article.