The Cancer Genome Atlas network sequenced 510 breast cancers exomes, identifying 4 distinct subtypes: luminal A (ER+ and/or PR+, HER2−), luminal B (ER+ and/or PR+, HER2+), HER2-enriched (ER−, PR−, HER2+), and basal-like (ER−, PR−, HER2−). This evidence concerns the gene ESR1 and breast cancer.