A cancer is a corpus of tissue that's moulded by an accumulation of abnormal cells. Usually, the cells in your body age, die, and are changed by new cells. As this procedure goes on, the tumor continues to produce as more and more cells are added to the mass. To diagnose a brain tumor, the doctor starts by asking questions about your symptoms and taking a personal and family health history. Then he or she performs a physical exam, including a neurological exam. If there's reason to suspect a brain tumor, the doctor may request any test. Tumor cells grow, even though the body does not need them, and unlike normal old cells, they don't die.