Medical professionals assign tumors “grades” to help your healthcare team communicate better, plan treatment, and predict outcomes. The grades (1-4) assess how cancerous the tumor cells are. A grade 1 tumor is the slowest growing and easiest to treat. A grade 4 tumor is the most cancerous and can be difficult to treat.
- Grade 1 tumors are the least cancerous and are usually associated with long-term survival. The tumors grow slowly and have an almost normal cellular appearance when viewed through a microscope. Surgery alone might be an effective treatment for this grade of tumor. Pilocytic astrocytoma is an example of a grade 1 tumor.
- Grade 2 tumors are relatively slow-growing and have a slightly abnormal cellular microscopic appearance. Some can spread into nearby normal tissue and reproduce themselves, and can become a higher grade tumor. Examples are grade 2 oligodendroglioma and grade 2 astrocytoma.
- Grade 3 tumors are by definition malignant (cancerous.) The cells of a grade 3 tumor are actively reproducing abnormal cells which grow into nearby normal brain tissue. These tumors tend to recur, or reproduce themselves, and may recur as a grade 3 or change to a grade 4. A cancer recurrence is defined as a return of cancer after treatment and after a period of time during which the cancer cannot be detected.
- Grade 4 are the most cancerous brain tumors. They reproduce rapidly, can have a bizarre cellular appearance when viewed under the microscope and easily grow into surrounding 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 center. Glioblastoma is the most common example of a grade 4 tumor.
A single tumor may contain several grades of cells. The highest or most cancerous grade of cell determines the tumor grade, even if most of the cells are a lower grade. Some tumors undergo changes. A lower-grade tumor might recur as a higher-grade tumor. Your doctor can tell you if your tumor might have this potential.