Study on Low Dose Temozolomide Plus Metformin or Placebo in Patient With Recurrent or Refractory Glioblastoma

Inclusion Criteria: 1. Progressive or recurrent Glioblastoma conformed by histopathological or radiological diagnosis. Progressive or recurrent Glioblastoma during or after standard therapy (Temozolomide after Temozolomide and radiation therapy; Stupp regimen) after histopathological diagnosis of Glioblastoma Recurrence or progression is diagnosed according to histopathological diagnosis or revised RANO(Response Assessment in Neuro-Oncology) criteria c 2. Karnofsky performance status(KPS) ≥ 60% 3. Age ≥ 19 years old 4. At least 4 weeks after operation or chemotherapy 5. Normal in hematological finding, liver and kidney function * Hematology ANC \> 1.500/mm³, Platelet \> 100,000/mm³, WBC \> 3×10\^9/L, Hemoglobin \> 9g/dL * Liver function Total Bilirubin level ≤ 1.5×ULN(in case of isolated hyperbilirubinemia ≤2.5 x ULN) AST / ALT \< 2.5×ULN * Renal function Serum creatinine ≤ 1.5mg/dL 6. Be informed of the nature of the study and obtained a written informed consent 7. A legal representative agrees to the trial when a subject is unable to communicate smoothly due to neurologic defect 8. If a fertile woman who has been confirmed negative to a urine or blood pregnancy test within 28 days prior to the trial Exclusion Criteria: 1. Pregnant or breast feeding 2. Cancer history within 5 years excluding cancer in the skin cells and cervix 3. Active infections within two weeks 4. Leptomeningeal metastasis 5. Patients diagnosed with diabetes 6. Hypersensitive or intolerance to Metformin 7. Patients who are currently taking Metformin, sulfonylureas, thiazolidinediones, and insulin, regardless of reason 8. Other serious diseases or medical conditions that include : * Patients who suffer from unstable heart disease despite treatment. * Patients having a heart attack within 6 months prior to the start of trial * Patients who suffer from severe nerve or psychosis that includes dementia or strokes. * Patients with an uncontrolled infection * Patient with uncontrolled hypertension, congestive heart failure, unstable angina, or incomplete arrhythmia 9. Those who have participated in other clinical trials may not recover from the toxicity of the treatment.