The study will evaluate the effectiveness of ixabepilone when given after doxorubicin plus cyclophosphamide (AC) compared to standard treatment of paclitaxel given after doxorubicin plus cyclophosphamide in patients with early stage breast cancer. In addition the study will verify predefined biomarkers as well as discover new biomarkers that could identify patients who are more likely to respond to ixabepilone than standard paclitaxel based therapy.