Trastuzumab emtansine in HER2-positive metastatic breast cancer: what is the best sequence?

Human epidermal receptor growth factor 2 (HER2, ERBB2) gene amplification occurs in about 15–20% of invasive breast cancers and is associated with biologically aggressive disease and poor overall survival in the absence of systemic therapy (1). The synthesis of trastuzumab, a humanized monoclonal antibody targeting the extracellular domain of HER2, was a major leap forward in the treatment of this disease.