Four distinct biochemical subgroups of breast cancer have emerged in recent years through comprehensive transcriptional profiling research: luminal A (ER+/HER2-/grade 1 or 2), luminal B (ER+/HER2-/grade 3), HER2 (HER2 + tumor) enriched, and basal-like (ER-/PR-/HER2-). The gene discussed is ERBB2; the disease is breast cancer.