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 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 brain tumors. Statistics suggest that brain cancer occurs infrequently and is likely to develop in about 22,000 new people per year in 2009, with about 13,000 deaths as estimated by the National Cancer Institute (NCI).
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 (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.
What is metastatic brain cancer?
Cancer cells that develop in a body organ such as the lung (primary cancer tissue type) can spread via the bloodstream or lymphatic system to other body organs such as the brain. Tumors formed by such cancer cells that spread (metastasize) to other organs are called metastatic tumors. Metastatic brain cancer is a mass of cells (tumor) that originated in another body organ and has spread into the brain tissue. Metastatic tumors in the brain are more common than primary brain tumors. They are usually named after the tissue or organ where the cancer first developed (for example, metastatic lung orbreast cancer tumors in the brain, which are the most common types found).
What causes brain cancer?
Primary brain tumors arise from many types of brain tissue (for example, glial cells, astrocytes, and other brain cell types). Metastatic brain cancer is caused by the spread of cancer cells from a body organ to the brain. However, the causes for the change from normal cells to cancer cells in both metastatic and primary brain tumors are not fully understood. Data gathered by research scientists show that people with certain risk factors are more likely to develop brain cancer. Individuals with risk factors such as having a job in an oil refinery, as a chemist, embalmer, or rubber-industry worker show higher rates of brain cancer. Some families have several members with brain cancer, but heredity as a cause for brain tumors has not been proven. Other risk factors such assmoking, radiation exposure, and viral infection (HIV) have been suggested but not proven to cause brain cancer. There is no good evidence that brain cancer is contagious, caused by head trauma, or caused by cell phone use. Although many lay press and Web articles claim that aspartame (artificial sweetener) causes brain cancer, as of 2009, the FDA maintains that it does not cause brain cancer and base their findings on over 100 toxicological and clinical studies regarding the sweetener's safety.