Brain Tumors: Grades

Neuroscience

Once your doctor knows you have a brain tumor, an important next step is to find out the grade of the tumor. The grade refers to how the cancer cells look under a microscope when compared with normal brain cells. Grade is determined by a pathologist when a tissue sample (biopsy) is sent to the lab.

How grading helps

The grade of your tumor will help your doctor know:

How quickly the tumor is likely to grow.
How likely it is that the tumor will spread to other parts of the brain.
How it might respond to treatment.
How likely it is to grow back after treatment.

Grades of brain tumors

There are many types of brain cancer. The World Health Organization grades tumors based on how abnormal cancer cells look under a microscope. It also considers how quickly a tumor grows and spreads. There are 4 grades used for brain tumors. Grades I and II are also called low-grade tumors. Grades III and IV are also called high-grade or anaplastic tumors. The grades are:

Grade I. This kind of tumor is the slowest growing and least likely to spread. Cells in a grade I tumor look a lot like normal brain cells. Your doctor may remove a grade I tumor with surgery, if it can be done safely. Or your doctor may follow the progress of a grade I tumor with yearly MRI scans.
Grade II. This kind of tumor has cells that are not normal when looked at under a microscope. They grow more slowly than Grade III and IV. They may invade the tissues around them. They tend to start growing faster over time. Even if they are fully removed with surgery, this kind of tumor can sometimes come back.
Grade III. This kind of tumor has cells that look more abnormal under the microscope, but there are no dead cells in it. This kind of tumor grows more quickly than Grade I and II tumor cells. They tend to spread into the tissues around it. When a grade III tumor is removed with surgery, it grows back faster than a grade II tumor. After surgery, additional treatment is usually needed using radiation therapy and chemotherapy.
Grade IV. This kind of tumor grows fast. It has blood vessels and areas of dead tissue. Grade IV tumor cells are very abnormal. They grow and spread quickly into other parts of the brain. Surgery can’t take out all of this tumor without harming the brain, so other types of treatment are often needed.