Here's the National Cancer Institute's explanation of the tumor:

Malignant gliomas are the most common primary brain tumor, accounting for
more than half of the more than 18,000 primary malignant brain tumors diagnosed
each year in the United States. These tumors are the second-most common cause of
cancer death in the 15 to 44 age group.

The outlook for patients with malignant gliomas is poor. Median survival for
patients with moderately severe (grade III) malignant gliomas is three to five
years. For patients with the most severe, aggressive form of malignant glioma
(grade IV glioma or glioblastoma multiforme), median survival is less than a
year.

Surgery is recommended for all operable brain tumors and is usually followed
by radiation therapy. Several studies have shown that adding chemotherapy to
radiation can improve patients' survival. In June 2004, after the completion of
the current study, researchers announced that adding the drug temozolomide
(Temodar®) to radiation therapy increased median survival in patients with
glioblastoma multiforme by about two months (see related story). This approach
is now considered the standard of care for the initial treatment of these
tumors.