This is a randomized, parallel-arm, open-label, multicentre, Phase II study to determine the efficacy and safety of lapatinib in combination with epirubicin and cyclophosphamide (EC90-L) followed by paclitaxel and lapatinib (PX-L) compared with EC90 followed by paclitaxel and trastuzumab (PX-T) as systemic neoadjuvant therapy for patients with previously untreated, operable, ErbB2-overexpressing, Stage I- IIIA breast cancer.