What is brain tumor?
Brain tumors are abnormal growths made up of cells whose growth and division are no longer under the control of the body. They can occur in the cerebrum (the largest portion of the brain responsible for planning movement, interpreting sensation, and controlling memory, learning, "thinking", and emotions), the cerebellum (controls balance and equilibrium), or the
brainstem (responsible for controlling heart rate, breathing, and consciousness).
A benign tumor does not contain cancer cells and usually, once removed, does not recur. Most benign brain tumors have clear borders, meaning they do not invade surrounding tissue. These tumors can, however, cause symptoms similar to cancerous tumors because of their size and location in the brain.
Malignant brain tumors contain cancer cells. Malignant brain tumors are usually fast growing and invade surrounding tissue. Malignant brain tumors very rarely spread to other areas of the body, but may recur after treatment. Sometimes, brain tumors that are not cancer are called malignant because of their size and location, and the damage they can do to vital functions of the brain.
Metastatic brain tumors are tumors that begin to grow in another part of the body, then spread to the brain through the bloodstream. Common types of cancer that can travel to the brain include lung cancer, breast cancer, melanoma (a type of skin cancer), and colon cancer. All of these cancers are considered malignant once they have spread to the brain.
Brain tumors may be primary or secondary. Primary brain tumors originate in the cells within or next to the brain. These tumors may be cancerous or noncancerous. Secondary brain tumors are metastases originating in another part of the body and thus are always cancerous.
Noncancerous tumors are named for the specific cells or tissues in which they originate. For example, hemangioblastomas originate in blood vessels ("hema" refers to blood vessels, and hemangioblasts are the cells that develop into blood vessel tissue). Some noncancerous tumors that originate in embryonic cells may be present at birth.
Most commonly, cancerous brain tumors are metastases from cancer that started in another part of the body. Metastases may grow in a single part of the brain or in several different parts. Many types of cancer - including breast cancer, lung cancer, cancer in the digestive tract, malignant melanoma, leukemia, and lymphoma - can spread to the brain. Lymphomas of the brain are common among people who have AIDS and, for unknown reasons, are becoming more common among people who have normal immune systems. The most common type of primary cancerous brain tumor is a glioma.
There are several types of primary brain cancers, each arising from a specific type of cell in the brain. Common primary brain cancers include astrocytomas (and their sub-types such as glioblastoma multiforme), oligodendogliomas, ependymomas, medulloblastomas, and CNS lymphomas. Brain cancers also vary in terms of their aggressiveness - i.e., how fast they grow and how readily they invade surrounding tissues. The most aggressive forms of brain cancer are called high grade, lesser degrees of aggressiveness are referred to as low grade. Tumor grade is determined by examining a sample of the tumor under the microscope.