Brain cancer differs from most other types of cancer, as they typically use a staging system to identify the location and spread of a tumour. However, there is no recommended staging system for brain tumours, as they usually do not spread beyond the CNS. Instead, a grading system is used to identify how cancerous a tumour is and how likely it is to grow. Typically, the lower the grade, the better the prognosis.
- Grade I: These tumours grow slowly, and are unlikely to spread. They are non-cancerous, and can often be removed with surgery.
- Grade II: These tumours are less likely to grow and spread, but are more likely to recur after treatment.
- Grade III: These tumours grow quickly, and are more likely to have rapidly dividing cells. They are less likely to have dead cells.
- Grade IV: The cells in these tumours are actively dividing, and these tumours grow and spread quickly. The tumour also has blood vessel growth and areas of dead tissue.
Low-grade tumours grow slowly, and don’t usually spread to other areas of the brain or surrounding tissues. Some low-grade tumours may develop into high-grade tumours. The cells in these tumours, if examined under a microscope, will look similar to normal cells.
High-grade tumours grow quickly, and can spread to nearby tissues and parts of the brain. However, if they start in the brain, they will rarely spread outside the CNS. The cells of these tumours look abnormal under a microscope, and can spread to other organs.
Information taken from Cancer.net.