Beyond sequence variation: assessment of copy number variation in adult glioblastoma through targeted tumor somatic profiling

Abstract

Glioblastoma is the most common primary malignancy of the adult central nervous system. Gliomagenesis involves a complex range of alterations, including sequence changes, copy number variations (CNVs), and epigenetic modifications, that have clinical implications for disease classification and prognosis. Thus, multiple testing modalities are required to support a complete diagnostic workup. The goal of this study was to streamline the multipart workflow by predicting both sequence changes and CNVs (specifically EGFR amplifications) from a single next-generation sequencing (NGS) test. Eighty-six primary and secondary glioblastomas were submitted for clinical NGS to report sequence variants from a concise panel of cancer-relevant genes. Most specimens underwent concomitant testing by methylation-specific polymerase chain reaction, immunohistochemistry, and fluorescence in situ hybridization. Using data generated during the course of clinical testing, we found that NGS-based variant predictions were concordant with immunohistochemistry and fluorescence in situ hybridization for IDH mutation and EGFR amplification status, respectively. We also noted that EGFR amplifications correlated with polysomy of chromosome 7, 19, and 20, and loss of PTEN and CDKN2A. EGFR-unamplified cases had lower rates of chromosome 7 polysomy, and PTEN and CDKN2A loss, but more CNVs overall. TP53, NF1, ATRX, and PDGFRA mutations were nearly exclusive to specimens without EGFR amplification. EGFR amplification was not associated with longer progression-free survival in this cohort, but amplifications were enriched in a group with slightly longer overall survival despite radiographic evidence of disease progression. Further study is needed to explore the mechanisms responsible for noted patterns of co-occurring variants and to correlate them with specific clinical outcomes.