GSTM1 and chronic myelogenous leukemia, BCR-ABL1 positive: The GSTM1 null genotype frequency was found to be slightly higher in the control group, (35% as opposed to 34% in CML patients), but this difference was not considered to be statistically significant (OR =0.975, 95% CI: 0.578-1.584; p- value = 0.863).