AdvertisementJohn McCain Was Diagnosed With A Glioblastoma, Among The Deadliest Of Cancers03:12Download AudioResumeJuly 20, 2017Jon HamiltonfacebookEmailGlioblastomas are the most common malignant brain tumor. About 12,000 people in the U.S. are diagnosed with the cancer every year. (Sherbrooke Connectivity Imaging Lab/Science Source)