Here, using different cancer cell lines, we sought to characterize the magnitude of the UPR in response to CFZ and CFZ+BET inhibitors by quantifying the changes in mRNA levels of representative genes in the PERK branch (ATF3, CHOP, and GADD34), IRE1 branch (IFRD1, ERN1, and ERO1LB), and the ATF6 branch (HERPUD1 and BiP). This evidence concerns the gene ATF3 and cancer.