PDE5A and glioblastoma: We found a similar phenomenon in our orthotopic GBM mouse models and demonstrated that inhibiting MDSCs using the PDE5 inhibitor tadalafil during and after cranial irradiation of the GBM-bearing mice prevented lymphopenia and improved tumor control.8 To translate our preclinical observations, we designed this pilot phase Ib study to combine tadalafil with standard chemoradiotherapy for newly diagnosed GBM.