However, we find nearly all deletions at 9p21.3 impact CDKN2B, CDKN2A, and MIR31HG. Using GBM cells and PDGXs, we find that altering the levels of endogenous miR-31 alone is sufficient to significantly alter GBM behavior in vitro and in vivo. Here, MIR31HG is linked to glioblastoma.