New directions in photodynamic therapy.

Photodynamic therapy (PDT), a treatment approach that makes use of a photosensitizer to generate a localized toxic species in diseased tissue, has recently become an approved treatment modality. So far, however, only a handful of photosensitizers have received regulatory approval and for a small number of diseases. This chapter outlines the major limitations of PDT and speculates on the possible improvements that are required in order to advance PDT to a front line therapy. Seven areas of improvements are discussed: drug selectivity, drug delivery, light delivery, combination therapies, pigmented tumors, other potential uses, and protocol optimization. For each area, current limitations are discussed, and further required studies are recommended.