OUTLINE: Patients receive trastuzumab (Herceptin) IV over 30-90 minutes followed by paclitaxel IV over 60 minutes on day 1. Treatment continues every 7 days for a total of 10 courses in the absence of disease progression or unacceptable toxicity. Patients undergo a modified radical mastectomy or a lumpectomy with axillary node dissection. Beginning 14 days after surgery, patients receive doxorubicin IV and cyclophosphamide IV over 15-30 minutes on day 1. Treatment repeats every 21 days for a total of 4 courses. After completion of chemotherapy, patients with hormone receptor-positive disease receive oral tamoxifen daily for 5 years. Patients are followed at 6 months.