human
I have a friend who has just been diagnosed with a brain tumor. What is a brain tumor and what are the different types?
assistant
A brain tumor is a mass of abnormal cells that grows in the brain or spinal cord. The most common type of brain tumor is called glioma, which is a cancerous tumor that starts in the glial cells of the brain. Other types of brain tumors include meningioma (a benign tumor that forms from the meninges, the protective membranes around the brain), astrocytoma (a tumor that forms from astrocytes, star-shaped cells in the brain), and ependymoma (a tumor that forms from ependymal cells, which line the ventricles of the brain).