Unlike other cancers, brain cancer is assigned a “grade” rather than a stage, based on how the cells look under the microscope. The most commonly used brain cancer grading system, developed by the World Health Organization (WHO), is as follows:
- Grade I. These tumors are slow-growing and unlikely to spread. They can often be cured with surgery.
- Grade II. These tumors are less likely to grow and spread but are more likely to come back after treatment.
- Grade III. These tumors are more likely to have rapidly dividing cells but no dead cells. They can grow quickly.
- Grade IV. In a grade IV tumor, cells in the tumor are actively dividing. In addition, the tumor has both blood vessel growth and areas of dead tissue. These tumors can grow and spread quickly.