C-erbB-2 (HER2/neu) protein overexpression or amplification has been noted in some solid tumors a molecular target for tumor suppression. C-erbB-2 protein is localized on the membrane surface and is classified in the EGFR family. Trastuzumab is a humanized monoclonal antibody which binds to the extracellular domain of the c-erbB-2 protein in breast cancer cells. Good responders to trastuzumab may be ICH 2 + and FISH positive breast tumors, and ICH 3 + cancer. The response rate is approximately 15% with single administration of trastuzumab. Combination therapy with paclitaxel for the treatment of patients with metastatic cancer may bring more than 60% response and improve time to disease progression. Congestive heart failure associated with trastuzumab may be severe, and combination therapy which includes anthracyclines increases the incidence and severity of cardiac dysfunction. Other toxicities include infusion reaction.