Photodynamic therapy--a new treatment option for epithelial malignancies of the skin.

Photodynamic therapy (PDT) is based on the activation of a photosensitizer by illumination with visible light, leading to photochemical tissue destruction or immunomodulation. The greatest disadvantage of systemic administration of photosensitizers is cutaneous photosensitization of the patients, which lasts for some months. An alternative approach for epithelial precancerous lesions, such as actinic keratoses and Bowen's disease, as well as for superficial skin tumors, such as basal cell carcinomas, is the topical application of sensitizers, especially 5-aminolevulinic acid. Topical PDT causes selective tissue necrosis and tumor destruction and produces excellent cosmetic results. The following article summarizes the main principles of PDT and provides a synopsis of the present status of the use of PDT for epithelial skin malignancies.