MMP9 and glioblastoma: Some circRNAs had been investigated in glioblastoma tissues, for instance, hypoxia-associated circDENND2A promoted glioblastoma aggressiveness by sponging miR-625-5p [13]; circular RNA circSCAF11 accelerated the glioblastoma tumorigenesis through the miR-421/SP1/VEGFA axis [14]; EIF4A3-induced circular RNA MMP9 (circMMP9) acted as a sponge of miR-124 and promoted glioblastoma multiforme cell tumorigenesis [11].