IDH1 and glioblastoma: identified four gene expression‐based subtypes (GeneExp‐Subtypes) by integrating genomic and transcriptomic data to demonstrate cell origin: (1) proneural (characterized by PDGFRA and IDH1 mutations, common in younger patients and secondary GBM); (2) neural (close to normal brain tissue with few mutations); (3) classical (marked by EGFR amplifications/mutations and PTEN deletions); and (4) mesenchymal (defined by NF1 abnormalities, altered neurofibromin expression, and mesenchymal/astrocytic differentiation gene expression).