Photodynamic therapy--indications and limits in malignant tumors treatment.

Photodynamic therapy (PDT) is a very promising technique used for the treatment of a variety of solid neoplasms, based on the formation of singlet oxygen induced by a photosensitizer after irradiation with visible light. The mechanism of interaction of the photosensitizers and light is discussed, along with the effects produced in the target tissue. PDT has been approved in many countries for the treatment of lung, esophageal, bladder, skin and head and neck cancers. The antitumor effects of this treatment result from the combination of direct tumor cell photodamage, destruction of tumor vasculature and activation of an immune response. The present status of clinical PDT is discussed along with the newer photosensitizers being used and their clinical roles. Despite the promising results from earlier clinical trials of PDT considerable additional work is needed to bring this new modality of treatment into modern clinical practice.