Due to the pivotal role of BRCA1 in mammary gland development and the large similarity between sporadic BLBCs and hereditary BRCA1-defective breast cancers, it has been postulated that BRCA1 deficiency attenuates breast CSC (BCSC) differentiation, resulting in accumulation of BCSCs in BLBCs [20]. Here, BRCA1 is linked to breast cancer.