Abstract: Provided are methods of targeting patient-specific oncogenes in extrachromosomal DNA (ecDNA) to treat glioma in a human. The present methods include identifying a drug that targets against an oncogene present in ecDNA of a human suffering from glioma, such as glioblastoma. The identified oncogenes present in ecDNA include MET, MET/CAPZA2, MDM2, CDK4, SOX2, PIK3CA, MECOM, PDGFRA, EGFR, MYCN, MYC, TERT, SMARCA4, RP56, FBXW7, CDK6, CCND2, ERBB2, BRCA1, and BAP1. The present methods include identifying a drug targeted against the ecDNA oncogene, which drug inhibits the function of the identified oncogene, so as to inhibit tumor growth or progression of the glioma in the human. Also provided are PDX mouse models to further identify and/or confirm patient-specific drugs that target the identified oncogene(s) present in ecDNA. Also provided are methods of diagnosing gliomas or recurrent gliomas and methods of screening or monitoring for recurrence of gliomas.