In this review, the already well-established mechanisms of ET resistance will be revisited, and the evidence underlying three pathways recently reported as putative mediators of ET resistance in BC—receptor activator of nuclear factor kappa B ligand (RANKL)/receptor activator of nuclear factor kappa B (RANK), nuclear factor kappa B (NFκB), and Notch—will be addressed. Here, NFKB1 is linked to breast cancer.