Once your healthcare provider knows you have a brain tumor, the next step is to find out the grade of the tumor. The grade refers to how the cancer cells look when compared to normal brain cells. Grade is determined when a tissue sample (biopsy) is sent to the lab. There, the tissue is looked at under a microscope and tests are done on it.
The grade of your tumor will help your healthcare provider 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
There are 4 grades of brain tumor. Grade I and II are also called low-grade tumors. Grade 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 healthcare provider may remove a grade I tumor with surgery, if it can be done safely. Or your healthcare provider 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 can grow and 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 into the tissues around it. When a grade III tumor is removed with surgery, it grows back faster than a grade II tumor.
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.