Trastuzumab for early breast cancer: current status and future directions.

The human epidermal growth factor receptor 2 (HER2) is overexpressed/amplified in up to 25% of breast cancer patients, and this feature is associated with an aggressive phenotype, a high recurrence rate, and reduced survival. Until recently, combination chemotherapy was the most effective and only adjuvant treatment for HER2-positive patients. Trastuzumab, a monoclonal antibody directed against the HER2 extracellular domain, has recently demonstrated highly reproducible and astonishing benefit in halving the recurrence rate and reducing mortality in five adjuvant breast cancer trials. But such unfettered success has come at a cost, both in terms of cardiotoxic risk and substantial financial burden. Though trastuzumab has been able to significantly improve clinical outcomes of many patients with early breast cancer, the reality is that an unacceptable proportion will still relapse. Beyond trastuzumab, what is the next step for these HER2-positive breast cancers? This review first discusses the individual results of the five adjuvant trastuzumab studies in terms of efficacy and safety, highlighting their similarities and differences. It also evaluates the current status of trastuzumab as a result of these studies and explores the possible future direction for HER2-positive breast cancers in light of recent advances in translational oncology.