GSTM1 and cancer: Due to different coding sites of amino acids, GSTM1-null (GSTM1 -/-) and GSTT1-null (GSTT1 -/-) present the detoxification functional gene deficiency, thus altering susceptibility to some cancers aroused by environmental and lifestyle factors.[14]GSTP1rs1695(AA, AG, GG), located on chromosome 11q13, is the most studied gene encoding the π class of enzymes.