WEE1 and glioblastoma: Three studies assessed intratumoral concentrations of protein kinase inhibitors (gefitinib, imatinib and lapatinib) in surgically resected tumor tissue of glioblastoma patients and found very variable tumor concentrations of these agents, which in part exceeded the corresponding plasma concentrations, which pointed to an increased permeability relative to normal brain [36, 39, 40].