DPP4 and neoplasm: Highly expressed circMET can induce EMT or degrade C-X-C motif chemokine ligand 10 (CXCL10) via the circMET/miR-30-5p/Snail/dipeptidyl peptidase 4 (DPP4) axis to reduce CD8+ T lymphocyte transport, thereby enhancing the formation of the immunosuppressive tumor microenvironment to promote tumor progression (79).