Photodynamic therapy (PDT) is an emerging treatment used to eradicate premalignant and early-stage cancer and reduce the tumour size in end-stage cancers. Its mechanism of action involves three key components: a photosensitizer, light (wavelength appropriate for the photosensitzer), and tissue oxygen. The combination of these three components leads to the destruction of tumor cells. It is an approved treatment for wet macular degeneration, and is also being investigated for treatment of psoriasis. Treatment of internal organs may be achieved through the use of endoscopes and fiber optic catheters to deliver light, and intravenously-administered photosensitizers...