ERBB2 and breast carcinoma: To determine if the constellations of mutations would be distinct between the HER2-positive and HER2-negative components of HER2 heterogeneous breast cancers, and to identify potential driver mutations restricted to the HER2-negative components, we subjected the HER2-positive and HER2-negative components of three cases (that is, T6, T11 and T12), for which sufficient DNA from frozen tumor and matched normal tissues was available, to whole exome sequencing.