Although both drugs also phosphorylated eIF2α in PC-9 cells, which are human lung cancer cell line and are extremely sensitive to EGFR inhibitors, the protective effect of TUDCA was not found in this cell line (S1 and S2 Figs), suggesting that TUDCA treatment would not disturb the anti-cancer efficacy of EGFR inhibitors in non-small cell lung cancer patients. Here, EGFR is linked to lung cancer.