IDH1 and central nervous system cancer: Interestingly, myeloid cells in IDH-O tumors are mostly comprised of microglia.29 In H3K27M-Mut gliomas, microglial transcriptional signatures are observed in pediatric patients, while adult patients exhibit more macrophage signatures.33 In all cases, a spectrum of macrophage to microglia phenotypes is observed, indicating that a binary classification of bone-marrow-derived macrophages and resident microglia as previously defined44 may not be sufficient to characterize these cells.