Here, we describe a case of a 49-year-old man with a GBM harboring a TERT promoter mutation... comprehensive genomic profiling by next-generation sequencing identified two rare mutations in EGFR: T790M and an exon 20 insertion. Based on these findings, the patient elected to undergo off-label therapy with osimertinib...no clinical response was observed, and the patient succumbed to the disease. The lack of response may be related to the specific nature of the EGFR mutations, and/or other unfavorable tumor biology overriding any benefit from osimertinib.