One way to classify a brain tumor is by the location from which it originates. Tumors that begin growing in the brain are known as primary brain tumors. Tumors that begin growing elsewhere in the body and then spread to the brain are referred to as metastatic, or secondary, brain tumors.
Metastatic brain tumors are far more common than primary brain tumors. According to the American Brain Tumor Association, of the 190,000+ Americans diagnosed with a brain tumor each year, slightly more than 40,000 have primary tumors, while the remaining 150,000 have metastatic tumors.
There are more than 120 different types of brain tumors, each of which is classified as either benign (low-grade) or malignant (high-grade). Cells from high-grade tumors look more abnormal and generally grow faster than cells from low-grade tumors. Neuropathologists are the specialists who examine brain tumors under a microscope to determine the tumor grade, based on the cells' appearance. Brain tumors range from grade I (low-grade) to IV (high-grade).
Typically, the following is true for each type of brain tumor:
Primary brain tumors are named according to the type of cells or part of the brain from which they originate. The most common primary brain tumors are gliomas. Gliomas arise from glial cells, or the supportive and connective cells of the central nervous system that surround neurons and provide support for, and insulation between, them. The main types of gliomas include the following:
Some types of brain tumors do not begin in glial cells. The most common of these tumors include the following:
Metastatic brain tumors (secondary brain tumors) start as cancer cells in another part of the body and metastasize, or spread, to the brain through the blood stream. The most common types of tumors that spread to the brain are lung, breast, colon and kidney cancers, as well as malignant melanoma (skin cancer). According to the Brain Tumor Society, brain metastases are the most common complication of cancer, occurring in 20 to 40 percent of all oncology patients. The above information was adapted from the National Cancer Institute's (NCI's) Web site.