Further, breast cancer can be subtyped including Luminal A (ER+ PRhigh HER2− Ki-67low), Luminal B (ER+ PR+ HER2+ or HER2− Ki-67high), HER2-enriched (ER− PR− HER2+), and triple negative or basal-like (ER− PR− HER2−) [104]. Here, ESR1 is linked to breast cancer.