Nevertheless, research has revealed that certain cancer cell lines maintain resistance to ferroptosis even after GPX4 inactivation, indicating the existence of additional ferroptosis defence mechanisms [26], such as the ferroptosis suppressor protein-1 (FSP1)-ubiquinone (CoQ10) system (the FSP1-CoQ10 system) [63, 64], the dihydroorotate dehydrogenase (DHODH)-ubiquinol (CoQH2) system (the DHODH-CoQH2 system) [65], and the GTP cyclohydroxylase-1 (GCH1)-tetrahydrobiopterin (BH4) system (the GCH1-BH4 system) [66]. This evidence concerns the gene GCH1 and cancer.