We hypothesized that loss of NF1 might sensitize cells to combined therapy, given preliminary data suggesting that a MEKi alone can induce growth suppression in some GBM cell lines.23 Here, we observed that loss of NF1 demonstrated a moderate correlation with sensitivity to MEKi monotherapy and combination therapy—a powerful observation given 10–15% of GBM has lost functional NF1 expression.1,21 Loss of neither the tumor suppressor PTEN nor TP53 correlated with sensitivity to combination therapy. This evidence concerns the gene TP53 and glioblastoma.