Trastuzumab is a humanized monoclonal antibody against the epidermal growth factor family oncogene, Her-2/neu. It has revolutionized therapy for the 15-20% of patients with metastatic breast cancer whose tumors have gene amplification for Her-2/neu. Results of clinical trials with single agent trastuzumab and in combination with paclitaxel, docetaxel, vinorelbine, gemcitabine and platinum salts have been encouraging. Durable remissions in excess of 5 years have occasionally been reported. Subjectively the side effect profile of this novel, targeted therapy, has been mild. Cardiac toxicity, while reported in combination regimens with anthracyclines tend to be easily manageable and not absolute contradictions to continuation of trastuzumab. Outside of clinical trials, however, anthracycline/trastuzumab combinations should be avoided. Preliminary results of trials with various combinations of chemotherapeutic agents have been promising while combinations with hormonal and other biologic therapy are ongoing. Trastuzumab is an exciting new monoclonal antibody with interesting anti-tumor activity in patients with Her-2/neu gene amplified breast cancer. We look forward to ongoing clinical trials combining trastuzumab with a broad array of other chemotherapeutic, hormonal and biological agents.