IDH1 and oligodendroglioma: In grades II and III gliomas, IDH2 mutations were overrepresented in oligodendrogliomas (22 IDH2 mutations out of 330 IDH mutated tumors; 6.7%), compared to astrocytomas (1/60; 1.7%) and mixed gliomas (6/176; 3.4%) (P = 0.049).