Brain tumors may not be cancers. They are different from other tumors. They grow only in the brain itself, and nearly never travel beyond the brain. Brain tumors involve the whole brain. Although they seem to grow nearby, yet tumor cells go around the brain and they can even be found on the opposite side of the brain and are always found beyond the tumor margins. True tumor margins are not existed. If we want to completely remove the brain tumors by local therapy, such as surgery, heat, cold or radiation are not possible at all. Brain tumors do not metastasize. Treatment should be limited solely to the brain. Brain tumors can be divided into 2 groups - malignant or nonmalignant. Malignant, or high-grade tumors have cancer cells in them. They grow quickly and attack the healthy tissue around them. Gradually a malignant tumor will damage or destroy the normal cells and interfere with their functions. They are hazardous. On the other hand, nonmalignant, or low-grade tumors can also attack the surrounding tissue, or coexist with the normal cells. Malignant tumors can cause severe neurological injuries, such as seizures, memory loss or behavioral changes. They can interfere with the regular and vital brain functions. Some of the malignant brain tumors are dangerous.