Here are some details about the malignant brain tumor of Senator Edward Kennedy.
The tumor is a glioma, so called because it arises from glial cells in the brain. The American Cancer Society website has an excellent backgrounder on brain and spinal cord cancers. An excerpt:
Glial cells are the main brain cells that can develop into cancer. Most adult brain tumors are glial cell cancers — sometimes called gliomas… Normal glial cells grow and divide very slowly. Most brain and spinal cord tumors develop from glial cells.