Although the combination of the triple-negative phenotype and the pathologic features described above have come to be considered characteristic of BRCA1-associated breast cancers, approximately 10 to 36% of breast cancers that occur in BRCA1 mutation carriers (BRCA1 carriers) are, in fact, ER-positive (ER+) [4,6,8,14,15]. Here, ESR1 is linked to breast cancer.