Photodynamic Therapy: Potential Applications for Exotic Animal Oncology

Photodynamic therapy (PDT) is a novel form of treatment for solid cancers. It relies on the systemic administration of a light-reactive drug (photosensitizer) to the patient. Through various mechanisms, the photosensitizer localizes to the malignant tissue. The photosensitizer is then activated by visible red light, often provided by a laser. The drug and light alone do not cause tissue damage; when the photosensitizer, light, and molecular oxygen are present together, the reactive oxygen species generated locally lead to apoptosis, vascular stasis, and subsequent ischemic necrosis, and inflammation. PDT is potentially useful for the treatment of exotic animals, because it has fewer adverse effects than radiation therapy or chemotherapy. Because PDT is typically a single session, there are fewer issues with repeated general anesthesia and vascular access. To date, experiences with PDT in exotic animals are limited, but preliminary reports suggest it will become a useful treatment in these species. Further knowledge of photosensitizer pharmacokinetics and tumor biology in exotic animals will be necessary to develop PDT into a useful cancer treatment modality.