Group 2: Up to 60 patients will be randomized to receive "Investigator's choice of salvage therapy" until they fulfill one of the criteria for study discontinuation (death, intolerable toxicities, investigator's judgment, or withdrawal of consent). "Investigator's choice of salvage therapy" will be limited to the following: temozolomide, lomustine, or carboplatin. The dose level for Investigator's choice salvage therapy (temozolomide, lomustine, or carboplatin), will be in accordance with the product label or institutional guidelines.