The present cohort of IDH-mutant astrocytomas with MMR mutations in the primary specimens also had significantly higher 2021 WHO grade at initial presentation than their MMR-wild-type counterparts (Table 1), and a significantly higher percentage of cases with mutations in MMR genes recurred at higher grade (Table 2), suggesting that MMR mutations may be driving cases toward higher histologic and molecular grade. The gene discussed is MRC1; the disease is astrocytoma (excluding glioblastoma).