Rostaporfin (tin ethyl etiopurpurin, REM-001, Sn(IV) etiopurpurin, Purlytin, SnET2), is a second generation photosensitizer drug. Rostaporfin is activated by red light with a wavelength of 664 nm. It is injected into the patient, where it distributes and selectively binds to plasma lipoproteins, which are produced in high concentrations by hyperproliferating cells such as cancer cells. After 24 h, the targeted cells are stimulated by red light to activate the compound. Rostaporfin preferentially accumulates in tumor cells due to an increased rate of metabolism. Upon exposure to a light source, this agent absorbs light, forming an extended high energy conformational state that produces high quantum yields of singlet oxygen with local cytotoxic effects.