Photodynamic therapy--coming of age.

With the advent of Phase III clinical trials, photodynamic therapy of solid tumors is about to gain respectability within the field of cancer therapy. This treatment modality uses visible light to activate tumor-localizing photosensitizers, and causes tissue destruction by generating highly cytotoxic molecular oxygen species. The almost universal tumor response achievable, mild general toxicity, and repeatability of treatment without loss of effectiveness account for its application in a wide variety of human neoplasms. A decade of basic and preclinical research has laid a solid foundation of knowledge of the mechanisms of the photodynamic effect, both on the cellular and tissue levels. Although open questions remain, these efforts have provided the rationale for new directions of development, such as the design of new photosensitizers and improved light sources. This report describes the events involved in photodynamic tumor destruction, emphasizing possible ways to improve this therapy in the future.