Other investigations have not observed a statistically significant effect on cyclophosphamide pharmacokinetics associated with the CYP2C19*2 SNP (Xie et al, 2006; Ekhart et al, 2008).Variants of the other CYP enzymes investigated in this study had no impact on outcome or toxicity in this cohort of breast cancer patients. This evidence concerns the gene CYP2C19 and breast cancer.