Brain tumors are classified into 4 grades according to their growing rate and how cancerous they are. It assists the treating doctors in finding the right treatment and medication planning. The grade is determined by a pathologist studying a small sample of the tissue from a biopsy under a microscope.

In the table below, the general characteristics of tumor cells of each grade are described. As a tumor does not consist of cells of one single grade, the highest grade of the cells is taken, even if the number of lower grade cells is much higher. Tumors from a lower grading may evolve into higher gradings

Grade 1:

These tumor cells are considered as the least malignant form. The growing rate is lowest among the tumor cells and on examining under a microscope, they show an almost normal appearance. Cells of this type are likely to be long-time survining cells. One possible treatment to remove them is surgery.

Grade 2:

Although classified as slow-growing cells, their growing rate is higher than Grade-1-cells. You can distinguish between Grade-1 and Grade 2 cells while viewing thorugh a microscope, as it shows  minor abnormalities. The cells can encroach on neighboring normal tissue and reproduce themselves, which can lead to a transformation to a higher level tumor.

Grade 3:

The tumor cells of this grade are actively affecting nearby healthy tissue to reproduce themselves, in contrast to the Grade-2-cells, which can adapt to this behavior but do not have to. These cells are classified as cancerous.

Grade 4:

The most malignant form of brain tumor cells are related to this grade. A very high reproduction rate and a high tendency of growing into surrounding brain cells are the characteristics of these cells. They can be easily graded as a cancerous cell due to its very abnormal appearance while examining under a microscope. To push their rapid growth further, they form new blood vessels.

Tumor cells, which recur after a treatment and/or cannot be detected for a certrain time and reappear afterwards, are usually assigned to Grade 3.