In grade 2 IDH-mutant oligodendrogliomas, scRNA-seq defined a developmental hierarchy in tumor cells, with a small population of stem-like proliferative glioma cells resembling neural stem/progenitor biology at one apex along with two differentiation trajectories, one towards mature oligodendrocyte-like and the other towards mature astrocyte-like apices [208]. The gene discussed is IDH1; the disease is oligodendroglioma.