Genomic features of IDH-mutant adult diffuse astrocytoma.

Abstract

e14032 Background: The fifth edition of the WHO Classification of Tumors of the Central Nervous System (CNS), published in 2021, which indicated that all IDH mutant diffuse astrocytic tumors are considered a single type (Astrocytoma, IDH-mutant) and are then graded as CNS WHO grade 2, 3, or 4. Besides, the guideline eliminates the term “Glioblastoma (GBM), IDH-mutant”. Moreover, grading is no longer entirely histological, since the presence of CDKN2A/B homozygous deletion results in a CNS WHO grade of 4, even in the absence of microvascular proliferation or necrosis. Therefore, more clinical and genomic characteristics of IDH-mutant astrocytoma under molecular typing need to be further studied. Methods: Adults pathological diagnosed with diffuse astrocytoma and glioblastoma in our Chinese dataset were identified retrospectively. All patients included in the analysis were tested for 131 CNS tumor-related genes (including IDH1/2), chromosomes 1p/19q and chromosomes 7/10. Results: 63 initial diagnosed IDH-mutant diffuse astrocytomas including 46 patients with grade 2-3 and 17 patients with uncertain grade. While, 5.2% of GBM (9/174) harbored IDH1/2 mutation which should be redefined as diffuse astrocytoma, IDH-mutant, WHO 4 grade. And these patients had a high frequency of CDKN2A/B homozygous deletion (88.9%, 8/9). In patients with 2-3 grade and unclear grade, CDKN2A/B homozygous deletion accounted for 18.7% (9/48) and 27.8% (5/18), respectively, which meant the grade of these diffuse astrocytomas should be revised to WHO 4 grade according to guideline. While mutation frequency of crucial prognosis factors in glioma, including chromosomes 7 loss, chromosomes 10 gain, EGFR amplification, PIK3CA/R1, PDGFRA amplification, CDK4 amplification, were 9.7%, 2.8%, 5.6%, 13.9%, 6.9% and 8.3% in all 72 astrocytomas, respectively. In addition, we found 83.3% (5/6) KDR copy number variant were occurred in which initially pathological diagnosed as IDH-mutant GBM. Conclusions: we conducted comprehensive analysis of IDH mutant diffuse astrocytoma. CDKN2A/B homozygous deletion as a specific grade-classified molecular marker could better re-distinguish about 20%-30% 2-3 grade and uncertain grade astrocytoma. KDR copy number variant may be a marker in IDH-mutant astrocytoma to identify the tumor which pathology is closer to GBM.