Our study has four interrelated aims: first, to investigate the frequency of the polymorphic variants CYP2C8*3, CYP2C8*4, CYP2C9*2, and CYP2C9*3 in a series of breast cancer patients; second, to construct CYP2C8/9 haplotypes; third to determine whether these genetic variants were associated with breast cancer characteristics of prognostic importance; and fourth, to investigate whether any of these genetic variants were associated with early breast cancer-related events. This evidence concerns the gene CYP2C9 and breast carcinoma.