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Brain tumors belong to a group of diverse tumors that affect the brain and spinal cord known as central nervous system neoplasms. A brain tumor is a mass of abnormal cells in the brain that have grown and multiplied in an uncontrolled fashion. Brain tumors that develop from various types of cells that make up the brain are called primary brain tumors. These types of brain tumors are usually localized (confined) to the brain itself and only rarely spread to other parts of the body. Metastatic brain tumors, also know as secondary brain tumors, originate from cancer cells in another part of the body (e.g., lung, breast) and spread to the brain through the bloodstream. The distinction between primary and secondary brain tumors is important from a clinical perspective because they are usually treated differently.

Approximately 50% of all primary brain tumors originate from specialized nerve cells in the brain called glial cells. Brain tumors that arise from glial cells are called gliomas. There are many different types of gliomas but the most common gliomas develop from glial cells called astrocytes. Primary brain tumors that develop from astrocytes are referred to as astrocytomas.

The World Health Organization (WHO) classifies astrocytomas into four distinct grades designated as Grade I, II, III, and IV (discussed in detail below) on the basis of how quickly the cells grow and spread and how the cells appear under a microscope. A glioblastoma, technically know as glioblastoma multiforme, is the fastest growing type of astrocytoma (Grade IV astrocytoma) that quickly spreads and invades nearby normal brain tissue and contains areas of dead cells (necrosis) in the center of the tumor.

Approximately 18,000 people in the United States are diagnosed each year with a malignant (cancerous) primary brain tumor. Glioblastoma multiforme (GM) is the most common type of primary malignant brain tumor in adults and accounts for about 50% to 60% of cases. Although GM can occur in all age groups, it is most commonly observed in adults 50 to 70 years in age. Less than 10% of childhood brain tumors are glioblastomas. Glioblastoma multiforme tends to occur more frequently in males than females by a ratio of about 3:2. According to the American Cancer Society, about 13,000 in the United States die each year from primary brain tumors.