ERBB2 and breast cancer: Trastuzumab, the first of a series of anti-HER2 agents, is a recombinant monoclonal antibody directed against the extracellular domain of the HER2 protein and has become the standard of care for patients with HER2-positive breast cancer, since it prolongs progression-free and overall survival in the adjuvant or metastatic settings [3, 4].