Grading helps us understand how aggressive, or malignant, a tumor is. Staging tells us if the tumor has spread and if so, how far.
There are four tumor grades — I, II, III, and IV. The higher the grade, the more malignant the tumor. Tumor grading helps the doctor, patient, and caregivers/family members to better understand the patient’s condition. It also helps the doctor plan treatment and predict outcome.
Below are description of the various tumor grades, based on the World Health Organization (WHO) grading system.
- Grade I: These are the least malignant tumors and are usually associated with long-term survival. They grow slowly and have an almost normal appearance when viewed through a microscope. Surgery alone may be an effective treatment for this grade tumor. Pilocytic astrocytoma, craniopharnygioma, and many tumors of neurons—gangliocytoma and ganglioglioma, for instance—are examples of grade I tumors.
- Grade II: These tumors are slow-growing and look slightly abnormal under a microscope. Some can spread into nearby normal tissue and recur, sometimes as a higher grade tumor.
- Grade III: These tumors are, by definition, malignant although there is not always a big difference between grade II and grade III tumors. The cells of a grade III tumor are actively reproducing abnormal cells, which grow into nearby normal brain tissue. These tumors tend to recur, often as a grade IV.
- Grade IV: These are the most malignant tumors. They reproduce rapidly, can have a bizarre appearance when viewed under the microscope, and easily grow into nearby normal brain tissue. These tumors form new blood vessels so they can maintain their rapid growth. They also have areas of dead cells in their centers. The glioblastoma multiforme is the most common example of a grade IV tumor.
Tumors can contain more than one grade of cell. The highest, or most malignant, grade of cell determines the grade of the tumor, even if most of the tumor is made up of lower-grade cells.
Staging for central nervous system (CNS) tumors is usually performed based on CT scans or MRI images, or by looking at the cerebrospinal fluid. Scans taken after surgery are used to determine if any tumor is left behind. CNS tumors that are usually prone to spread are studied with both scan images and laboratory tests. Patients with medulloblastoma, for example, will often have their cerebrospinal fluid examined for the presence of tumor cells. These patients also require spinal cord scans because of that tumor’s tendency to spread to the spinal cord.
Generally speaking, the lower the tumor grade, the better the chance of recovery.
It is important to note that the information provided here is basic and does not take the place of an in-person assessment by a physician. If you have any questions about how brain tumors are diagnosed, please contact your doctor.