The CYP genes with the lowest expression in the TCGA breast cancer cohort were: CYP1A2 (0.010), CYP3A43 (0.029), CYP3A7 (0.033), CYP2C9 (0.044) and CYP3A4 (0.044). This evidence concerns the gene CYP2C9 and breast carcinoma.