OBJECTIVES: I. Evaluate the safety of paclitaxel plus trastuzumab (Herceptin) followed by adjuvant chemotherapy in women with node positive stage II or IIIa breast cancer with HER2 overexpression. II. Evaluate the safety of long term trastuzumab (Herceptin) in this patient population.

OUTLINE: This is a randomized study. Patients are stratified according to radiotherapy (none planned vs planned to breast or chest wall). Patients are randomized to one of two treatment arms. Arm I: Patients receive paclitaxel IV over 3 hours immediately followed by trastuzumab (Herceptin) IV over 30-90 minutes on day 1. Paclitaxel repeats every 3 weeks for 4 courses and trastuzumab (Herceptin) repeats weekly for 10 courses. At 3 weeks following paclitaxel and trastuzumab (Herceptin), patients receive doxorubicin IV and cyclophosphamide IV over 1 hour every 3 weeks for 4 courses. Following chemotherapy, estrogen receptor (ER) positive and/or progesterone receptor (PR) positive patients receive oral tamoxifen twice daily for 5 years. Arm II: Patients receive same therapy as in Arm I, except for additional trastuzumab (Herceptin) IV weekly beginning within 3 weeks following completion of chemotherapy and local therapy and continuing for 1 year. ER and/or PR positive patients receive tamoxifen as in Arm I but may be concurrent with trastuzumab (Herceptin). Following completion of doxorubicin and cyclophosphamide, post lumpectomy and post mastectomy patients may receive local radiotherapy daily for 5-6 weeks. Treatment continues in the absence of disease progression or unacceptable toxicity. Patients are followed every 3 months for 1 year, every 6 months for 2 years, and then annually thereafter.

PROJECTED ACCRUAL: A total of 200 patients (100 per treatment arm) will be accrued for this study within 1 year.