During the period of this study, MGMT-methylated glioblastoma patients diagnosed with a small volume recurrence with a maximum tumor dimension of 5 cm were enrolled onto an ongoing clinical trial (NCT03743662) testing the combination of nivolumab and fractionated stereotactic radiosurgery, systemic therapy alone trials (NCT04421378), or combination trials of immunotherapy and tumor-treating fields (NCT03430791). This evidence concerns the gene MGMT and glioblastoma.