BRCA1-mutated breast tumors also show a tendency to be pathologically distinguished from other breast tumors with regard to expression of estrogen receptors (ER), as the majority of breast tumors in BRCA1 carriers are ER-negative, while only about 20–30% of other breast tumors (including BRCA2-mutated) are ER-negative [14,15]. Here, ESR1 is linked to breast neoplasm.