Firstly, it was a single-center study with a relatively small sample size, especially the low numbers of patients with oligodendroglioma and IDH-mutant grade 4 glioma—which precluded more informative analyses such as the comparison of oligodendroglioma vs. astrocytoma and GBM vs. IDH-mutant grade 4 glioma. Here, IDH2 is linked to central nervous system cancer.