ERBB2 and breast cancer: The breast oncology community now 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).