HSP90B1 and cancer: This suggests that two pathways may be involved in the regulation of GRP94: glycosylation inhibition mediated and the one mediated by Ca2+ [31], where GRP94 expression promotes radio-chemotolerance in cancer cells during the maintenance of cellular Ca2+ homeostasis when combating ER stress, after going through cleavage by calpain, simultaneously preventing apoptosis [9].