In the same vein, GRP78 maintains breast cancer cell stemness via the β-catenin/ABCG2 signaling pathway [137,138], with extracellular GRP78 also implicated in tumor cell stemness [139,140], re-echoing the possibility of a multicompartment intracellular epichaperome network that connects extracellularly, further shaping tumor cell behavior. Here, ABCG2 is linked to neoplasm.