Molecular Determinants of Prognosis and Evolution in Diffuse-Lower Grade Astrocytomas

Low grade astrocytomas (LGAs) are classified based on the mutational status of the isocitrate dehydrogenase (IDH) gene. While IDH wild-type (WT) LGAs evolve rapidly to glioblastoma, mutant tumors generally have a more indolent course. To identify potential drivers of the differential progression of LGAs, we analyzed transcriptomes from The Cancer Genome Atlas. Compared to mutant LGAs, platelet-derived growth factor (PDGF) signaling is enriched in WT cases, and PDGFA is the top overexpressed gene in the pathway. Putative mechanisms for differential PDGFA expression included copy number gains of chromosome 7 in WT cases and methylation of the PDGFA promoter in mutant LGAs. Additionally, we found that high PDGFA expression is associated with aneuploidy, immunosuppressive features, and worse prognosis, and that WT LGAs use multiple means to inactivate the p53 pathway to progress to GBM. Our work highlights the contribution of PDGF gene family towards the unique behaviour of LGAs. STATEMENT OF SIGNIFICANCEThis study of gene expression in LGAs suggests that differential regulation of the PDGF pathway may underlie the different natural histories of IDH WT and IDH mutant LGAs including divergent evolutionary trajectories to GBM. This insight may inspire new therapeutic strategies to suppress the transformation of LGAs to higher-grade cancers.