Based on their expression, four distinct types of BC can be distinguished: luminal A (ER+ and/or PR+, HER2-), luminal B (ER+ and/or PR+, HER2+/-), HER2-positive (ER-, PR-, HER2+) and TNBC (ER-, PR-, HER2-) [93,94]. This evidence concerns the gene ESR1 and breast cancer.