Since the 2014 ISN-Haarlem classification and the WHO 2016 Classification of Tumors of the Central Nervous System [1], most tumors previously characterized as oligodendrogliomas based on conventional histologic features are now classified into OGs with the characteristic double molecular signature of IDH mutation and 1p/19q codeletion, or into ASs, the latter including 4 potential subgroups:. The gene discussed is IDH2; the disease is oligodendroglioma.