Using expression profiling Perou et al.[1] described several molecular subtypes among which are three main categories: Luminal cancers that express Estrogen (ER) and/or Progesterone (PR) Receptors but lack Human Epidermal Growth Factor Receptor-2 (HER2); HER2-overexpressing cancers; and basal-like cancers that lack ER, PR and HER2. This evidence concerns the gene ESR1 and cancer.