The CYP2E1-mediated ER stress and UPR were assessed in breast cancer cells by monitoring the luciferase activity of the pCAX-HA-2xXBP1deltaDBD9anATG)-Luc-F reporter in breast cancer cell lines transfected with PCDNA3, CYP2E1, scrambled RNAi, or CYP2E1 shRNA. The gene discussed is CYP2E1; the disease is breast cancer.