IDH1 and central nervous system cancer: In our study, we observed 100% of G-CIMP-low at recurrence as grade IV tumors; however, not all grade IV gliomas resembled G-CIMP-low, suggesting that grade may not be the only determinant of G-CIMP-low cell identity in this rare subset of aggressive IDH mutant 1p-19q non-Codel gliomas.