MMP9 and glioblastoma: We found that among the circRNAs involved in GBM, circ-MMP9(Wang et al., 2018b), hsa_circ_0067934 (Xin et al., 2019), hsa_circ_0001801 (Chen et al., 2019), circ-PARP4 (Zhou J. et al., 2021), circ-PITX1 (Cao et al., 2021), hsa_circ_0006168 (Wang T. et al., 2021), hsa_circ_0001588 (Wang Q. et al., 2021) and circ-MELK (Zhou F. et al., 2021) can regulate GBM invasion and metastasis by modulating the EMT process.