This 2-arm, randomized, phase III study will investigate the efficacy and safety of the addition of rindopepimut (an experimental cancer vaccine that may act to promote anti-cancer effects in patients who have tumors that express the EGFRvIII protein) to the current standard of care (temozolomide) in patients with recently diagnosed glioblastoma, a type of brain cancer.

All patients will be administered temozolomide, the standard treatment for glioblastoma. Half the patients will be randomly assigned to receive rindopepimut and half the patients will be randomly assigned to receive a control called keyhole limpet hemocyanin.

Patients will be treated in a blinded fashion (neither the patient or the doctor will know which arm of the study the patient is on). Patients will be treated until disease progression or intolerance to therapy and all patients will be followed for survival.

The purpose of this research study is to find out whether adding an experimental vaccine called rindopepimut (also known as CDX-110) to the commonly used chemotherapy drug temozolomide can help improve the life expectancy of patients with newly diagnosed, resected EGFRvIII positive glioblastoma.

The duration of participation in this study may be up to 5 years. After you are screened and enrolled in the study, you will be administered temozolomide and either rindopepimut/GM-CSF or KLH until either disease progression or intolerance to the medications. If your tumor progresses while on this study, your doctor may treat you with other therapies that are not part of the study.

Inclusion Criteria-

Among other criteria, patients must meet the following conditions to be eligible for the study:

1. Adult patients, ≥ 18 years old
2. Newly diagnosed glioblastoma
3. Attempted surgical resection followed by conventional chemoradiation
4. Documented EGFRvIII positive tumor status by a Sponsor designated laboratory
5. No evidence of progressive disease from the post-operative period to the post-chemoradiation period
6. Candidate for, and agrees to receive, adjuvant (maintenance) temozolomide therapy
7. Systemic corticosteroid therapy at ≤2 mg of dexamethasone or equivalent per day for at least 3 days prior to randomization
8. WHO-ECOG Performance Status ≤ 2
9. Patients of childbearing/reproductive potential will be instructed to use birth control as defined by your doctor.

Exclusion Criteria-

Among other criteria, patients who meet the following conditions are NOT eligible for the study:

1. Stereotactic biopsy only (without further surgical resection)
2. Presence of diffuse leptomeningeal disease, gliomatosis cerebri, or infratentorial disease.
3. History, presence, or suspicion of metastatic disease
4. Patients who have received any additional treatment for glioblastoma, aside from surgical resection and chemoradiation with temozolomide
5. Active systemic infection requiring treatment
6. History of any malignancy (other than glioblastoma) during the last three years except non-melanoma skin cancer, in situ cervical cancer, treated superficial bladder cancer, cured, early-stage prostate cancer in a patient with PSA level less than ULN,or other carcinoma in situ that has been adequately treated and cured.
7. Planned major surgery
8. Evidence of current drug or alcohol abuse
9. Known allergy or hypersensitivity to keyhole limpet hemocyanin (KLH), GM-CSF (sargramostim; LEUKINE®), polysorbate 80 or yeast derived products, or a history of anaphylactic reactions to shellfish proteins
10. Severe acute or chronic medical or psychiatric condition or laboratory abnormality that could increase the risk associated with participating in a clinical trial
11. Women who are pregnant or lactating