EGFR and glioblastoma: The epidermal growth factor receptor (EGFR) is the most frequently altered oncogene in GBM, amplified in around half of all tumors.2 High-copy number amplification of EGFR is common in GBM and often takes the form of extrachromosomal circular DNA (eccDNA) fragments.3EGFR (hyper)amplification can be followed by additional genomic molecular abnormalities in the gene, mainly in its extracellular domain (ECD).