Padeliporfin (formerly known as WST-11) is novel and potent vascular-acting photosensitizer with potential antineoplastic activity. It is composed of a water-soluble, palladium-substituted bacteriochlorophyll analogue. Paldeliporfin is activated locally upon administration, when the tumor bed is exposed to low-power laser light; reactive oxygen species (ROS) are formed upon activation and ROS-mediated necrosis may occur at the site of interaction between the photosensitizer, light and oxygen. Vascular-targeted photodynamic therapy (VTP) with padeliporfin may allow tumor-site specific cytotoxicity while sparing adjacent normal tissues. (NCI Thesaurus).