In MCF-7 and MDA-MB-231 breast cancer cells, Grp78 was upregulated upon tamoxifen treatment, leading to resistance; however, Grp78-inhibitory 1 enhanced apoptosis induction by tamoxifen in these cells, accompanied by suppression of tamoxifen-induced phosphor-GSK-3β, which is a downstream factor of Akt signaling [69]. Here, HSPA5 is linked to breast cancer.