Following the biopsy lab analysis, your doctor will share the results with you, which will include the type and grade of the tumor. Primary brain tumors are named based on the type of cells they formed in, while the grade of a tumor indicates the difference between slow-growing and fast-growing tumors. Tumor grades are based on how abnormal the cancer cells look under a microscope or by looking at changes in genes or proteins. Knowing the grade helps to predict a tumor’s likely behavior.

  • Grade I (low-grade) – The tumor cells look more like normal cells under a microscope and grow and spread more slowly than grade II, III, and IV tumor cells. They rarely spread into nearby tissues. Grade I brain tumors may be cured if they are completely removed by surgery.
  • Grade II — The tumor cells grow and spread more slowly than grade III and IV tumor cells. They may spread into nearby tissue and may recur (come back). Some tumors may become a higher-grade tumor.
  • Grade III — The tumor cells look very different from normal cells under a microscope and grow more quickly than grade I and II tumor cells. They are likely to spread into nearby tissue.
  • Grade IV (high-grade) — The tumor cells do not look like normal cells under a microscope and grow and spread very quickly. There may be areas of dead cells in the tumor. Grade IV tumors usually cannot be cured.

Low-grade tumors can become high-grade tumors. While a tumor may show characteristics from one or more tumor grades, doctors treat patients based on the highest-level tumor grade.

Source: National Cancer Institute

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