Clinician's modern approaches to molecular genetic diagnosis of glioblastomas

The article is devoted to the issue of molecular genetic diagnosis of cerebral glioblastomas. Despite significant advances in neurooncology, little progress has been made in prolonging the life of patients with cerebral glioblastoma, and a significant part of the effectiveness of treatment depends on the recognition of two prognostic biomarkers: mutations of the isocitrate dehydrogenase (IDH) promoter and the methylation of the O6-methylguanine methyl transferase (MGMT) promoter. The article summarizes the data of world and domestic clinical studies, allowing to supplement the histological characteristics of primary glioblastomas with genetic markers: the presence of the TERT mutation, EFGR amplification, loss of PTEN function, LOH 10q, and the presence of the BRAF mutation. It should be noted that the amplification of EGFR, causing resistance to apoptotic stimuli and alkylating chemotherapy with Temozolomide, attracts much attention as a therapeutic target. The frequency of occurrence of the TERT mutation is 90% of all tumors of various genesis, most often the TERT mutation is found in oligodendroglioma or primary glioblastoma. Loss of heterozygosity in the region of localization of the PTEN gene is observed in many types of sporadic tumors, including more than 40% of glioblastomas. Mutations in this gene are found in tumors of the brain, endometrium, prostate, kidney, and mammary gland. The presence of a PTEN mutation is a poor prognostic factor. LOH 22q is much more common in secondary glioblastomas (82%) than in primary glioblastomas (41%). Among brain tumors, the BRAF mutation is most common with pleomorphic xanastrocytoma (60-70%).The BRAF V600E mutation was found in epithelioid glioblastoma, which is a rare and aggressive type of glioblastoma, characterized by an unfavorable prognosis (about 6 months) and frequent leptomeningeal spread. Thus, knowledge of the molecular mechanisms of carcinogenesis will enable a personalized approach to treatment with glioblastomas of the brain.

PATH-23. GENOMIC LANDSCAPE OF IDH-MUTANT PRIMARY GLIOBLASTOMAS SHOWS DISTINCT CLINICAL AND MOLECULAR FEATURES AND THAT CDKN2A SHOULD BE SUPPLEMENTED WITH MGMTp AND G-CIMP FOR PRECISE PROGNOSTICATION

There have only been rare studies of IDH-mutant primary glioblastomas (IDH-mutant astrocytoma IV); there were one or two studies on secondary glioblastomas. In a cohort of 70 cases, we conducted clinical analysis, methylation profiling, RNA sequencing, targeted sequencing, and TERTp seqeuncing on available FFPE tissues. Median follow-up was 58.2 months (n= 60). IDH-mutant primary glioblastomas had longer median OS (30.4 months) and median PFS (25.9 months) than IDH-mutant secondary glioblastomas as in the literature or established databases. MGMTp methylated cases had better OS (p= 0.001) and it was an independent prognosticator. We previously showed G-CIMP to be an independent prognostic marker for IDH-mutant glioblastomas (NOA 2019). Although CDKN2A deletion was an independent prognostic marker for poorer OS (p= 0.036) and PFS (p= 0.005), MGMTp methylation had a trend of superseding CDKN2A deletion (p= 0.055) for prognostication and G-CIMP subgroups could similarly partially supersede CDKN2A deletion (p= 0.582). Hence, CDKN2A deletion should be supplemented with these two biomarkers for finer prognostication. Targeted sequencing (n= 55) showed that there were more ATRX (35/55, 64%), TP53 (31/55, 56%), KMT2D (18/55, 33%), POLE (11/55, 20%) and MSH6 (7/55, 13%) mutations, but fewer TERTp (3/69, 4%) and PTEN (1/55, 2%) mutations than IDH-wildtype glioblastomas as from literature and databases. CNVs revealed by methylomes (n= 53) and mutations (n= 55) showed that there were more PDGFRA (amplification: 9/53, 17%, mutation: 10/55, 18%) alterations, but fewer MET (amplification: 3/53, 6%, mutation: 4/55, 7%) alterations and hypermutated (6/55, 11%) cases than IDH-mutant secondary glioblastomas from literature. GISTIC analysis revealed amplifications of CCND2, CDK4, MYC, and PDGFRA, deletions of CDKN2A, RB1, and chromosome 10q to be significant CNVs (q< 0.05). There were few EGFR amplifications (2/53, 4%), which was different from regular glioblastomas. RNA sequencing (n= 42) showed few fusions (4/42, 10%), which was different from IDH-mutant secondary glioblastomas.