Staging describes how far cancer has spread from where it began. Tumors that begin in the brain are not staged, because while they may spread to other parts of the central nervous system, they rarely spread to distant organs or lymph nodes.
Grade means how different the tumor cells look from normal cells when the pathologist examines them under a microscope. Brain tumors are graded from 1 to 4, as classified by the World Health Organization (WHO), with the higher numbers indicating faster growth and greater aggressiveness.
- Grade 1: The cells look nearly like normal brain cells, and they grow slowly.
- Grade 2: Compared with cells in a Grade I tumor, these cells look less like normal cells.
- Grade 3: Cells in the tumor look very different from normal cells. The abnormal cells are actively growing (anaplastic).
- Grade 4: The tumor has cells that look the most abnormal and tend to grow quickly.
Cells from low-grade tumors (grades 1 and 2) look more normal and generally grow more slowly than cells from high-grade tumors (grades 3 and 4). Over time, a low-grade tumor may become a high-grade tumor. However, the change to a high-grade tumor happens more often in adults than in children.