GPX3 and cancer: Additionally, catalase (CAT) and glutathione peroxidase 3 and 4 (GPX3 and 4) in shEPOR tumors were 3.5, 5, and 3.6 times lower than those in shSCR tumors (p<0.001) (Figure 2B), implying that the proportion of shEPOR A549 cancer cells in the tumor biopsies respire less than shSCR A549 cancer cells.