The emergence of trastuzumab has drastically changed therapy for breast cancer. Trastuzumab (Herceptin; Genentech) is a recombinant humanized monoclonal antibody that targets an epitope in the extracellular domain of the human epidermal growth factor receptor 2 (HER2) protein. HER2 is a member of a family of four transmembrane receptor tyrosine kinases that regulate cell growth, survival, and differentiation via multiple signal transduction pathways. Overexpression of HER2 or amplification of the HER2 gene occurs in 20%-30% of human breast cancers. Preclinical models have demonstrated that this antibody has significant antitumor activity as a single agent, and it also has a synergy with certain chemotherapeutic drugs. Phase II and III clinical trials performed in women with metastatic breast cancers that overexpress HER2 have shown trastuzumab to have clinical activity when used as monotherapy, while also improving survival when used as a first-line therapy in combination with chemotherapy. At present, clinical investigations are focusing attention on the efficacy of trastuzumab in both the adjuvant and neoadjuvant setting, as well as in the metastatic setting. In this review, we describe the developments and current status of trastuzumab-based treatment for breast cancer.
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