PATH-21. IDH-MUTATED, 19q DELETED, TP53 MUTATED ANAPLASTIC GLIOMAS CONSTITUTE A SUBGROUP THAT LOOK LIKE AND BEHAVE LIKE ANAPLASTIC OLIGODENDROGLIOMAS

Lower grade gliomas with IDH-mutation are divided into two major entities by genetic alteration pattern: astrocytomas with TP53/ATRX mutations and oligodendrogliomas with 1p/19q codeleted/TERT promotor mutations. Clinicopathological features of those two entities are different, with the latter mostly showing distinctive histological features with isomorphic round nuclei with perinuclear halo, and conferring longer survival. However, we noticed that a small subgroup of the astrocytomas demonstrate clinicopathological features similar to oligodendrogliomas.

42 IDH-mutated anaplastic diffuse gliomas were examined on molecular genetic profiles, histological features, and clinical outcome (OS).

There were 23 1p/19q codeleted tumors and 19 non-codeleted tumors. Of the 19 non-codeleted tumors, 7 showed 19q deletion only, with all having TP53 mutation as well, and showed oligodendroglia-like tumor cells with occasional neuronal differentiation, the histological features commonly observed in oligodendrogliomas. Furthermore, the prognoses of those 7 tumors were better than other anaplastic astrocytomas, with medial OSs of 105 mo. vs. 44 months.

Therefore, the 19q-deleted, IDH-mutated, TP53 mutated diffuse gliomas may constitute a subgroup that look like oligodendrogliomas and behave like oligodendrogliomas, albeit diagnosed as astrocytomas by the current diagnostic criteria.