ERBB2 and breast cancer: The ‘big data’ revolution has dramatically enhanced our appreciation of the molecular heterogeneity of breast cancer, further stratifying the disease into biologically and clinically meaningful subtypes, including six or more intrinsic subtypes (normal, claudin-low, luminals A and B, HER2 enriched and basal) [2,3,4,5]; four triple negative molecular subtypes (basal-like 1, basal-like 2, mesenchymal and luminal androgen receptor) [6]; and, ten integrative clusters captured by combined transcriptional and DNA copy number profiling [7].