Grade I (low-grade) - The tumor grows slowly, has cells that look a lot like normal cells, and rarely spreads into nearby tissues. Grade I brain tumors may be cured if they are completely removed by surgery.
Grade II - The tumor grows slowly, but may spread into nearby tissue and may recur (come back). Some tumors may become a higher-grade tumor.
Grade III - The tumor grows quickly, is likely to spread into nearby tissue, and the tumor cells look very different from normal cells.
Grade IV (high-grade) - The tumor grows and spreads very quickly and the cells do not look like normal cells. There may be areas of dead cells in the tumor. Grade IV tumors usually cannot be cured.
The following types of tumors can form in the brain or spinal cord:
An astrocytic tumor begins in star-shaped brain cells called astrocytes, which help keep nerve cells healthy. An astrocyte is a type of glial cell. Glial cells sometimes form tumors called gliomas. Astrocytic tumors include the following:
Brain stem glioma (usually high grade): A brain stem glioma forms in the brain stem, which is the part of the brain connected to the spinal cord. It is often a high-grade tumor, which spreads widely through the brain stem and is hard to cure. Brain stem gliomas are rare in adults. (See the PDQ summary on Childhood Brain Stem Glioma Treatment for more information.)
Pineal astrocytic tumor (any grade): A pineal astrocytic tumor forms in tissue around the pineal gland and may be any grade. The pineal gland is a tiny organ in the brain that makes melatonin, a hormone that helps control the sleeping and waking cycle.
Pilocytic astrocytoma (grade I): A pilocytic astrocytoma grows slowly in the brain or spinal cord. It may be in the form of a cyst and rarely spreads into nearby tissues. Pilocytic astrocytomas can often be cured.
Diffuse astrocytoma (grade II): A diffuse astrocytoma grows slowly, but often spreads into nearby tissues. The tumor cells look something like normal cells. In some cases, a diffuse astrocytoma can be cured. It is also called a low-grade diffuse astrocytoma.
Anaplastic astrocytoma (grade III): An anaplastic astrocytoma grows quickly and spreads into nearby tissues. The tumor cells look different from normal cells. This type of tumor usually cannot be cured. An anaplastic astrocytoma is also called a malignant astrocytoma or high-grade astrocytoma.
Glioblastoma (grade IV): A glioblastoma grows and spreads very quickly. The tumor cells look very different from normal cells. This type of tumor usually cannot be cured. It is also called glioblastoma multiforme.