A brain tumor is an abnormal growth of tissue in the brain. The tumor can either originate in the brain itself or come from another part of the body and travel to the brain (metastasize). Brain tumors may be classified as either benign (non-cancerous) or malignant (cancerous), depending on their behavior.

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, are usually fast growing and invade surrounding tissue. They 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, location and the damage they can do to vital functions of the brain.