GSTM1 and cancer: The frequencies of homozygous deletion genotypes of GSTM1 and GSTT1 are about 50% and 14% in Caucasians, and the homozygous deletion genotypes of both GSTM1 and GSTT1 were reported to be associated with risk for a variety of cancers and may be linked to alterations in drug metabolism (Hengstler et al., 1998).