Figure 1. The principles of PDT.
A photosensitizer (PS) is administered systemically or topically. After a period of systemic PS distribution it selectively accumulates in the tumor. Irradiation activates the PS and in the presence of molecular oxygen triggers a photochemical reaction that culminates in the production of 1O2. Irreparable damage to cellular macromolecules leads to tumor cell death via an apoptotic, necrotic or autophagic mechanism, accompanied by induction of an acute local inflammatory reaction that participates in the removal of dead cells, restoration of normal tissue homeostasis and sometimes in the development of systemic immunity.