ERBB2 and breast cancer: The breast oncology community currently describes breast cancer in terms of intrinsic biologic subtypes, and at least four subtypes are defined: basal-like (ER−/PR−/HER2−), luminal A (ER+/HER2−/grade 1 or 2), luminal B (ER+/HER2−/grade 3) and HER2 enriched (any HER2+ tumor).