Amplification of the HER2 gene and/or overexpression of its protein product have been found in up to 25% to 30% of human breast cancers and have been shown to be associated with poorer outcomes compared to 'HER2 normal' breast cancer. Research has focused on developing therapies directed to the HER2 receptor and its pathway. These include the monoclonal antibody trastuzumab, which has improved outcomes when used in patients with both advanced and early breast cancer. Lapatinib is a small-molecule tyrosine kinase inhibitor which has demonstrated activity in advanced breast cancer and is currently being evaluated in early stage disease. We discuss the therapeutic rationale and clinical trial experience with these agents. Other novel and emerging strategies targeting the HER2 receptor and its pathway are also discussed. These strategies include novel HER2 antibodies and small-molecule inhibitors, antibody-drug conjugates, agents targeting downstream components of the HER2 signaling pathway, and heat shock protein 90 (HSP90) inhibitors.
Keywords: HER2; breast cancer; human epidermal growth factor receptor 2; lapatinib; trastuzumab.