GSTM3 (Glutathione S-Transferase Mu 3) is a gene that encodes an enzyme in the glutathione S-transferase family, which helps detoxify harmful substances. It plays a crucial role in breaking down carcinogens, drugs, and oxidative stress byproducts. Variations in GSTM3 may affect an individual's risk of developing cancer, neurodegenerative diseases, and other conditions linked to detoxification processes.