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Brain Tumor Grading

After examining a biopsy sample of a brain tumor’s cells, the pathologist will determine the exact type of tumor it is and assign it a grade based on how likely it is to grow and spread. (If the doctors cannot perform a biopsy, they will diagnose the tumor based on other test results.)

The World Health Organization defines four grades of brain tumors.
Grade I

  • These tumors are regarded as benign, or non-cancerous, though they may slowly grow.

  • Their cells appear close to normal under a microscope.

  • The borders of the tumor are distinct.

  • Benign tumors can cause problems when they compress the brain.

  • Grade I tumors are rare in adults, and are associated with long-term survival.

Grade II

  • These slowly-growing tumors may spread to nearby tissue.

  • Their cells appear slightly abnormal under a microscope.

  • Grade II tumors may return as a more aggressive tumor after therapy.

Grade III

  • These tumors are considered malignant, or cancerous.

  • The cells are abnormal and reproducing, with spread into healthy brain tissue.

  • Grade III tumors are likely to recur, coming back as a more aggressive tumor.

Grade IV

  • These aggressive tumors are the most serious because of their rapid growth and spread.

  • The cells are very abnormal, and the tumor creates new blood vessels as it grows.

  • Grade IV tumors may have a core of dead cells (necrosis).

Why Tumors Change Grades

The grade of a brain tumor might change due to changes within the tumor itself or if the first biopsy doesn’t capture the entire tumor. A change from a low- to a high-grade tumor happens more often in adults than in children.

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