ESR1 and breast cancer: The classification was based on the IHC subtyping system of BC described by Sung et al. [24]: 178 (44%) luminal A (ER+ and/or PR+, Her2−), 90 (22%) luminal B (ER+ and/or PR+, Her2+), 62 (15%) H2BC (Her2-enriched; (ER−, PR−, Her2+)), and 77 (19%) TN (triple-negative; (ER−, PR−, Her2−)).