gms | German Medical Science

Objective: While astrocytoma and oligodendroglioma are histologically and genetically well-defined entities, oligoastrocytomas (OA) appear less clearly defined. As per the 2016 update of the classification of CNS tumors, we reclassified OA diagnosed histologically before addressing molecular molecular markers IDH1r132H, TP53, ATRX and FUBP-1 loss and segregating OA into two groups, genetically matching oligodendroglioma or astrocytoma, respectively.

Methods: We included patients that had undergone cranial tumor removal within our neurosurgical department and were diagnosed with oligoastrocytoma. IDH1R132H-, TP53-, ATRX- and FUBP-1-status were assessed by immunohistochemistry. We further reviewed patient charts and correlated neuropathological findings with outcome.

Results: We identified 56 patients diagnosed with oligoastrocytoma. Median age was 41.1 years (IQR 34-47), 19 patients (33.9%) were suffering from recurrent tumor. Complete resection was achieved in 25 patients (44.6%), 28 patients (50%) underwent postoperative radiotherapy, 20 patients (35.7%) underwent postoperative chemotherapy and 8 patients underwent combined radio-/chemotherapy (14.3%). Of the patients, 15 patients (26.8%) were initially diagnosed with a WHO° II tumor and 41 patients (73.8%) were diagnosed with a WHO° III tumor. Between WHO°II and WHO°III oligoastrocytoma, mo significant differences were observed regarding PFS (p=0.17) and OS (p=0.39). When considering molecular markers, and reapplying the updated classification of 2016, we diagnosed 2 patients (3.6%) with WHO° II Oligodendroglioma, 13 patients (23.2%) with WHO° II diffuse astrocytoma, 5 patients (8.9%) with WHO° III anaplastic oligodendroglioma and 36 patients (64.3%) with WHO ° III anaplastic astrocytoma. Upon reclassification, a significant difference was observed regarding progression-free survival (p=0.04) and overall survival (p=0.04) between the abovemtioned groups. In multivariate analysis, independent factors associated with progression-free survival were postoperative chemotherapy (p=0.03) and histology per the 2016 classification (p=0.048). Independent factors associated with overall survival were age (p=0.01), recurrent tumor (p<0.01) and neuropathological findings per the 2016 classification (p=0.03).

Conclusion: Reclassification of oligoastrocytoma per the updated 2016 classification of CNS tumors into two groups, genetically matching oligodendroglioma or astrocytoma allows for a better correlation with outcome. Moreover, this grouping is an independent factor associated with progression-free and overall survival.