Glutathione S-transferase M1 (GSTM1) is an important enzyme in the body’s detoxification pathway. GSTM1 conjugates glutathione to molecules (drugs, environmental toxins, carcinogens etc.) bound for excretion. GSTM1 is mainly responsible for binding toxins in joints and for binding carcinogens.
GSTM1 plays a role in the detoxification of metabolites of environmental carcinogens including tobacco smoke. Some studies suggest that people with common polymorphisms of these genes may have an increased susceptibility to a range of different cancers, including lung cancer. (Source 1)