A lipophilic, second-generation, chlorin-based photosensitizer. Upon intravenous administration, HPPH selectively accumulates in the cytoplasm of cancer or pre-cancerous cells. When laser light is applied, a photodynamic reaction between HPPH and oxygen occurs, resulting in the production of cytotoxic free radicals and singlet oxygen and free radical-mediated cell death. Compared to the first-generation photosensitizer porfimer sodium, HPPH shows improved pharmacokinetic properties and causes only mild skin photosensitivity which declines rapidly within a few days after administration.