Glossary

Astrocytes, which can develop in any part of the brain or spinal cord, are star-shaped glial cells where the tumor originates. It can be any grade, but in adults, it most often arises in the cerebrum. More than 75 percent of all gliomas are astrocytomas. Commonly astrocytomas are classified in four grades:

* Grade I astrocytoma:
* Called low-grade glioma
* Slow growing
* Well-defined borders
* Rare and almost exclusively found in children or teens

* Grade II astrocytoma:
* Rarely spreads to other parts of central nervous system
* Slow growing
* Borders not defined
* Common among men and women, 20s to 50s

* Grade III astrocytoma:
* Sometimes called a high-grade or an anaplastic astrocytoma
* More aggressive than grade II astrocytoma
* Cells not uniform
* Invades other tissue
* More common in men than women

* Grade IV astrocytoma:
* Called a glioblastoma or malignant astrocytic glioma
* Most invasive type of glial tumor
* Composed of several different cells, making it difficult to treat
* Grows rapidly and invades other tissue
* May have evolved from low-grade tumor
* Common in young adults and among men and women, 50s to 70s
* Account for 30 percent of all primary brain tumors
* More common in men

Astrocytoma, which account for 3,000 new cases a year in the U.S., is the most common form of brain cancer. It represents 23 percent of primary brain tumors. The annual U.S. incidence rate: three per 100,000.