TDO2 and central nervous system cancer: AQP4 plays an important role in proliferation, invasiveness, migration, and apoptosis in glioma cells.22 To explore the potential relationship between IDO1/TDO and glioma migration and invasion, paraffin-embedded tissue sections with IDO1 or TDO-positive expression were divided into four groups of IDO1-low group, IDO1-high group, TDO-low group, and TDO-high group according to the expression levels of IDO1 and TDO (for definition standards, see the Materials and methods section), and the expression level of AQP4 in these four groups was examined.