Using global gene-expression profiling, breast cancers can be molecularly classified into five intrinsic subtypes: luminal A (LumA), luminal B (LumB), HER2 enriched (HER2-E), basal-like (BL), and normal-like (NL)3,4, although these subtypes do not represent distinct disease entities but, rather, exist on a continuum. The gene discussed is ERBB2; the disease is breast cancer.