Global gene expression profiling was subsequently used to molecularly classify breast tumors into various subtypes: luminal A (ER+ and/or PR+/−); luminal B (ER+ and/or PR+/−) and either HER2 overexpressing or not; basal-like (triple negative breast cancers (TNBC), do not express hormone receptors nor overexpress HER2; and normal-like. The gene discussed is ESR1; the disease is triple-negative breast carcinoma.