ABSTRACT
Astroblastomas are rare primary brain tumors, diagnosed based on histologic features. Not currently assigned a WHO grade, they typically display indolent behavior, with occasional variants taking a more aggressive course. We characterized the immunohistochemical characteristics, copy number (high-resolution array comparative genomic hybridization, OncoCopy) and mutational profile (targeted next-generation exome sequencing, OncoPanel) of a cohort of seven biopsies from four patients to identify recurrent genomic events that may help distinguish astroblastomas from other more common high-grade gliomas. We found that tumor histology was variable across patients and between primary and recurrent tumor samples. No common molecular features were identified among the four tumors. Mutations commonly observed in astrocytic tumors (IDH1/2, TP53, ATRX, and PTEN) or ependymoma were not identified. However one case with rapid clinical progression displayed mutations more commonly associated with GBM (NF1(N1054H/K63)*, PIK3CA(R38H) and ERG(A403T)). Conversely, another case, originally classified as glioblastoma with nine-year survival before recurrence, lacked a GBM mutational profile. Other mutations frequently seen in lower grade gliomas (BCOR, BCORL1, ERBB3, MYB, ATM) were also present in several tumors. Copy number changes were variable across tumors. Our findings indicate that astroblastomas have variable growth patterns and morphologic features, posing significant challenges to accurate classification in the absence of diagnostically specific copy number alterations and molecular features. Their histopathologic overlap with glioblastoma will likely confound the observation of long-term GBM "survivors". Further genomic profiling is needed to determine whether these tumors represent a distinct entity and to guide management strategies.
Subject(s)
Brain Neoplasms/genetics , Genome-Wide Association Study/methods , Neoplasm Recurrence, Local/genetics , Neoplasms, Neuroepithelial/genetics , Adult , Brain Neoplasms/pathology , Comparative Genomic Hybridization , DNA Mutational Analysis , Female , Gene Dosage , High-Throughput Nucleotide Sequencing , Humans , Male , Middle Aged , Neoplasm Recurrence, Local/pathology , Neoplasms, Neuroepithelial/pathology , Sequence Analysis, DNAABSTRACT
IMPORTANCE: Conclusive intraoperative pathologic confirmation of diffuse infiltrative glioma guides the decision to pursue definitive neurosurgical resection. Establishing the intraoperative diagnosis by histologic analysis can be difficult in low-cellularity infiltrative gliomas. Therefore, we developed a rapid and sensitive genotyping assay to detect somatic single-nucleotide variants in the telomerase reverse transcriptase (TERT) promoter and isocitrate dehydrogenase 1 (IDH1). OBSERVATIONS: This assay was applied to tissue samples from 190 patients with diffuse gliomas, including archived fixed and frozen specimens and tissue obtained intraoperatively. Results demonstrated 96% sensitivity (95% CI, 90%-99%) and 100% specificity (95% CI, 95%-100%) for World Health Organization grades II and III gliomas. In a series of live cases, glioma-defining mutations could be identified within 60 minutes, which could facilitate the diagnosis in an intraoperative timeframe. CONCLUSIONS AND RELEVANCE: The genotyping method described herein can establish the diagnosis of low-cellularity tumors like glioma and could be adapted to the point-of-care diagnosis of other lesions that are similarly defined by highly recurrent somatic mutations.
