PATH-17. POSSIBLE ASSOCIATION BETWEEN OLIGODENDROGLIAL HISTOLOGICAL FEATURES OF IDHMUT/CODEL LOWER GRADE GLIOMAS AND PATIENT'S FAVORABLE PROGNOSIS, BUT NOT IN IDHMUT/NONCODEL AND IDH-WILDTYPE TUMORS

Abstract

Abstract Comprehensive diagnostic using histological and molecular characteristics began to be implemented in WHO 2016 but the relevance of oligodendroglial histological features to patients’ prognoses is still controversial. To elucidate the connection between oligodroglial histology and patient’s prognoses we analyzed 93 LrGGs resected for about 2 decades were reassessed for histological features based on WHO2007 with special interest to pure oligodendroglial diagnosis (namely, oligodendroglioma or anaplastic oligodendroglioma) and presence of classic for oligodendroglioma (CFO) features. Those histological features, patients’ OS, and tumor chromosomal/genetic characteristics were correlated each other in each of the 3 IDH-1p/19q based molecular groups. The reassessed morphology-based diagnosis was shown to be most strict for astrocytic, but loosened for oligodendroglial tumors as compared with the original institutional diagnoses and WHO2016. The pure oligodendroglial diagnosis by reassessment was associated with longer OS in IDHmut/codel group, but not in IDHmut/noncodel and IDH-wildtype groups. The presence of CFO was not associated with patients’ OS in any molecular groups. Gain of 8q was associated with the oligodendroglial diagnosis in IDHmut/noncodel group. Neither the oligodendroglial diagnosis nor CFO was predictive for the methylation status of the MGMT gene in any of the 3 molecular groups. NGS of the IDHmut/codel tumors suggested that mutations in the FUBP1 and CIC genes might be associated with poor prognosis. The oligodendroglial histological feature is not independently predictive for either patients’ prognosis or chemotherapeutic response in LrGGs, except the oligodendroglial diagnosis in IDHmut/codel tumors.