What is brain cancer?

Brain cancer is a disease of the brain in which cancer cells (malignant) arise in the brain tissue. Cancer cells grow to form a mass of cancer tissue (tumor) that interferes with brain functions such as muscle control, sensation, memory, and other normal body functions. Tumors composed of cancer cells are called malignant tumors, and those composed of mainly noncancerous cells are called benign tumors. Cancer cells that develop from brain tissue are called primary brain tumors while tumors that spread from other body sites to the brain are termed metastatic or secondary brain tumors. Statistics suggest that brain cancer occurs infrequently and is likely to develop in about 23,000 new people per year with about 13,000 deaths as estimated by the National Cancer Institute (NCI) and American Cancer Society.
Not all brain tumors are alike, even if they arise from the same type of brain tissue. Tumors are assigned a grade depending on how the cells in the tumor appear microscopically. The grade also provides insight as to the cell's growth rate. NCI lists the following grades:

• Grade I: The tissue is benign. The cells look nearly like normal brain cells, and they grow slowly.
• Grade II: The tissue is malignant. The cells look less like normal cells than do the cells in a grade I tumor.
• Grade III: The malignant tissue has cells that look very different from normal cells. The abnormal cells are actively growing and have a distinctly abnormal appearance (anaplastic).
• Grade IV: The malignant tissue has cells that look most abnormal and tend to grow quickly.

The most common primary brain tumors are usually named for the brain tissue type from which they originally developed. These are gliomas, meningiomas, pituitary adenomas, vestibular schwannomas, and primitive neuroectodermal tumors (medulloblastomas). Gliomas have several subtypes which include astrocytomas, oligodendrogliomas, ependymomas, and choroid plexus papillomas. When the grades are coupled with the tumor name, it gives doctors a better understanding about the severity of the brain cancer. For example, a grade III (anaplastic) glioma is an aggressive tumor, while an acoustic neuroma is a grade I benign tumor. However, even benign tumors can cause serious problems if they grow big enough to cause increased intracranial pressure or obstruct vascular structures or cerebrospinal fluid flow.
Brain cancers are staged (stage describes the extent of the cancer) according to their cell type and grade because they seldom spread to other organs, while other cancers, such as breast or lung cancer, are staged according to so-called TMN staging which is based on the location and spread of cancer cells. In general, these cancer stages range from 0 to 4, with stage 4 indicating the cancer has spread to another organ (highest stage).