GSTM1 and breast cancer: In two reports based on the same sample, women with breast cancer with null mutations for GSTM1 and GSTT1 had reduced risk of death compared to women with alleles present, (Ambrosone et al. 2001) and a reduction in mortality risk for women homozygous for the variant GSTP1 Val allele compared to those homozygous for the Ile allele (Sweeney et al. 2000; Yang et al. 2005).