Analysis of pooled cohorts of diffusely infiltrating gliomas with paired MGMT promoter status evaluation in both paired primary and recurrent tumors [17, 38, 104, 133] demonstrates that ~ 15% of cases have discrepancies in MGMT promoter methylation status and may either develop or lose promoter methylation at the time of recurrence (Fig. 4b), although the available sample size is too small to make definitive conclusions on the prognostic or treatment effects of this change. The gene discussed is MGMT; the disease is central nervous system cancer.