Similar as previously reported [7], HIF-2α may account for the chemoresistance, since reduction of HIF-2α positive proportion of CSCs occurred simultaneously with regained cell apoptosis so as to sensitivities to chemotherapeutic drugs within USP9X-knockdown CDDP and PTX-resistant cancer cells (Fig. 2, and Supplementary Fig. S5H). This evidence concerns the gene EPAS1 and cancer.