Despite advances in diagnosis and treatment, breast cancer still remains a major cause of cancer deaths. Metastatic breast cancer (MBC) is virtually incurable, with median survival of 18 to 24 months. The HER2 gene encodes a growth factor membrane receptor that is overexpressed in 25-30% of MBC cases and is associated with aggressive metastasis and poor prognosis. Transtuzumab (HerceptinR) is a humanised monoclonal antibody against HER2 that has proven efficacy as a single-agent therapeutic for MBC. This randomised phase III trial analysed the effect of adding transtuzumab to standard first-line chemotherapy (CT) for MBC.