Tumor ablation with photodynamic therapy: introduction to mechanism and clinical applications.

Photodynamic therapy (PDT) has been used to treat cancer for more than 25 years. Although the focus has been primarily on surface or superficial lesions, there has been a rapid growth in its application to the treatment of deeper parenchymal malignancies. The photochemical reaction consists of a photosensitizer, which, when irradiated by light at a specific wavelength, generates a cytotoxic oxygen singlet. The end result is an efficient induction of cell death, primarily through apoptosis, microvascular damage, and an antitumor immune response. PDT is currently being used in the treatment of many cancers including lung cancer, head and neck cancers, liver metastases, cholangiocarcinoma, and prostate cancer. The growing body of evidence concerning its efficacy, the increasing use of imaging to guide PDT, and the innate minimally invasive characteristics of PDT suggest that it should become an important addition to the growing array of techniques in interventional oncology.