Staging refers to the extent or spread of cancer. Currently, there is no standard staging system for primary brain tumors. Brain tumors that begin in the brain may spread to other parts of the central nervous system, but they rarely spread to distant organs or lymph nodes. The treatment of brain tumors is based on a number of factors, including:
- The brain cell type from which the tumor originated (e.g. astrocyte, oligodendrocyte)
- Location in the brain where the tumor formed
- The amount of cancer left after surgery
- The patient’s age and condition
- The grade of the tumor. Grade is determined by how the tumor appears to the pathologist under the microscope, and indicates the tumor’s aggressiveness. For example, astrocytomas are graded from I to IV with the higher numbers indicating faster growth and greater malignancy.
Brain tumors are grouped by grade. The grade of a tumor refers to the way the cells look under a microscope:
- Grade I: The tissue is benign. The cells look nearly like normal brain cells, and they grow slowly.
- Grade II: The tissue is malignant. The cells look less like normal cells than do the cells in a Grade I tumor.
- Grade III: The malignant tissue has cells that look very different from normal cells. The abnormal cells are actively growing (anaplastic).
- Grade IV: The malignant tissue has cells that look most abnormal and tend to grow quickly.
Cells from low-grade tumors (grades I and II) look more normal and generally grow more slowly than cells from high-grade tumors (grades III and IV). Over time, a low-grade tumor may become a highgrade tumor. However, the change to a high-grade tumor happens more often among adults than children.