DPP4 and neoplasm: Aberrant expressions of ferroptosis-related genes (FRGs), such as tumor protein p53 (TP53) (Junttila and Evan, 2009), Fanconi anemia complementation group D2 (FANCD2) (Han et al., 2017), glutathione peroxidase 4 (GPX4) (Liu H. et al., 2018), heat shock protein beta 1 (HSPB1) (Arrigo and Gibert, 2012), and dipeptidyl-peptidase-4 (DPP4) (Enz et al., 2019), were reported to be correlated with tumor genesis and progression.