Thirty-one BC specimens (11 HER2+, 10 HER2−, and 10 HER2-low) were routinely analyzed using IHC and ISH, and were selected and analyzed using NGS for gene mutations including ESR1, PIK3CA, AKT1, ERBB2, TP53, BRCA1, and BRCA2, CNV, and MSI. This evidence concerns the gene ESR1 and breast cancer.