Specific chemotherapy by aromatase inhibitors (i.e., Tamoxifen ®) for estrogen-positive breast cancer or monoclonal antibody (i.e., Trastuzumab ®) for HER2 positive breast cancer can be useful when used in combination with anthracyclines (Doxorubicin, Epirubicin) and taxanes (Paclitaxel, Taxol®, and Docetaxel, Taxotere®) [3,4]. The gene discussed is CYP19A1; the disease is breast cancer.