MGMT and central nervous system cancer: An ongoing window of opportunity study with the same drug in recurrent and progressive glioma and GBM (clinicaltrials.gov, NCT04047303) could be leveraged to gain information, not only to test the penetration of the BBB by the drug, but also to provide functional evidence for the efficiency of BETi-mediated MGMT depletion (RNA and sustained depletion of protein) and of other candidates of interest.