Heterogeneous HER2 Amplification-a New Clinical Category of HER2-Positive Breast Cancer?

HER2 amplification heterogeneity is associated with resistance to trastuzumab emtansine in the neoadjuvant setting, emphasizing the importance of assessing whether heterogeneous HER2-positive cancers require different treatment pathways. See related article by Metzger Filho et al., p. 2474 .