Rostaporfin (also known as REM-001, tin ethyl etiopurpurin, Sn(IV) etiopurpurin, Purlytin, SnET2), is a synthetic purpurin with photosensitizing activity. 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.