• Age ≥ 18 years of age at the time of entry into the study

• Newly diagnosed supratentorial GBM, WHO grade 4, IDH wildtype, MGMT unmethylated (high grade glioma with molecular features of GBM will be eligible under WHO 4 malignant glioma) with residual radiographic non-contrast enhancing disease on the post-2 cycles of adjuvant TMZ MRI amenable to catheter placement. The residual radiographic contrast enhancing disease is ≤ 3 cm in maximal diameter in any plane.

• Patient must have completed standard of care radiation therapy (typically 59.4-60 Gy over approximately 6 weeks duration if under 65 years old and a minimum of 40 Gy over 3 weeks duration if 65 years or older) in combination with TMZ and 2 cycles of post-radiation, adjuvant TMZ. For patients known to be MGMT promoter unmethylated prior to start of radiation therapy, patients are not mandated to have received TMZ in combination to radiation therapy prior to participating in this trial.

• Karnofsky Performance Score (KPS) \> 70%

• Able to undergo brain MRI wiht and without contrast

• Hemoglobin ≥ 9 g/dl prior to catheter placement

• Platelet count ≥ 100,000/µL unsupported. Because of risks of intracranial hemorrhage with catheter placement, platelet count ≥ 125,000/µl is required for the patient to undergo biopsy and catheter insertion, which can be attained with the help of platelet transfusion

• Neutrophil count ≥ 1000 prior to catheter placement

• Creatinine ≤ 1.5 x normal range prior to catheter placement

⁃ Total bilirubin ≤ 1.5 x upper limit of normal (ULN) prior to catheter placement (Exception: Participant has known or suspected Gilbert's Syndrome for which additional lab testing of direct and/or indirect bilirubin supports this diagnosis. In these instances, a total bilirubin of ≤ 3.0 x ULN is acceptable.)

⁃ AST/ALT ≤ 2.5 x ULN

⁃ PT and PTT ≤ 1.2 x normal prior to biopsy. Patients with prior history of thrombosis/embolism are allowed to be on anticoagulation, understanding that anticoagulation will be held in the perioperative period per the neurosurgical team's recommendations. Low molecular weight heparin (LMWH) is preferred. If a patient is on warfarin, the international normalized ratio (INR) is to be obtained and value should be below 2.0 prior to biopsy.

⁃ Patient or partner(s) meets one of the following criteria:

∙ Non-childbearing potential (i.e. not sexually active, physiologically incapable of becoming pregnant, including any person who is post-menopausal or surgically sterile, or any person who has had a vasectomy). Surgically sterile people are defined as those with a documented hysterectomy and/or bilateral oophorectomy or tubal ligation. Postmenopausal for purposes of this study is defined as 1 year without menses.; or

‣ Childbearing potential and agrees to use one of the following methods of birth control: approved hormonal contraceptives (e.g. birth control pills, patches, implants, or infusions), an intrauterine device, or a barrier method of contraception (e.g. a condom or diaphragm) used with spermicide

⁃ A signed ICF approved by the IRB will be required for patient enrollment into the study. Patients must be able to read and understand the informed consent document and must sign the informed consent indicating that they are aware of the investigational nature of this study