HER-2 belongs to a family of four transmembrane receptor tyrosine kinases that mediate growth, differentiation and survival of cells. HER-2 overexpression and amplification occurs in approximately 15 to 25 % of breast cancers and is associated with aggressive tumour behaviour. Herceptin (trastuzumab), a humanized monoclonal antibody directed against the extracellular domain of the HER-2 receptor, has been shown to have clinical activity in HER-2-positive advanced breast cancer when administered alone or in combination with chemotherapy. It has been approved for HER-2-positive metastatic breast cancer by the United States Food and Drug Administration in 1998 and in the countries of the European Union in 2000. Recently, promising results of the four randomized international multicenter trials evaluating the therapeutic benefit of Herceptin in the adjuvant treatment of HER-2-positive primary breast cancer have been reported. Data of the first planned interim analysis of the studies showed significantly improved disease-free survival in patients assigned to one year of Herceptin compared to the control groups even after short term follow up. These results caused an immediate wave of demand for Herceptin in adjuvant therapy. Results of these studies are critically reviewed. Furthermore, the available preliminary results from studies using Herceptin in the primary (neoadjuvant) therapy of HER-2-positive breast cancer are addressed and possible implications for HER-2 testing are discussed.
