IDH1 and astrocytoma (excluding glioblastoma): They are classified histologically and molecularly as oligodendroglioma harboring mutation of IDH1 or IDH2 (IDH-mutant) and codeletion of chromosomal 1p and 19q arms, or astrocytoma harboring IDH mutation often accompanied by ATRX loss and TP53 mutation.1,2 Typically, IDH-mutant LGGs are treated with surgical resection followed by chemotherapy,3 though patients considered high risk with an age older than 40 or subtotal resection or biopsy only may receive chemo-radiotherapy,4,5 most commonly with temozolomide (TMZ).