All eligible patients must have biopsy-proven invasive breast cancer and must also have biopsy-proven involvement of the axillary lymph nodes at initial presentation. Biopsy-proven involvement of the axillary lymph nodes at initial presentation will be based on fine needle aspiration (FNA) cytology, core/Tru-cut biopsy, or pre-treatment SLN biopsy. All eligible patients will have undergone preoperative neoadjuvant systemic chemotherapy.