Brain Tumors

Pathology & Grading 

A pathology report provides you and your health care team with essential information about the specific characteristics of your tumor. This information serves as a guide to plan the treatment most likely to be effective for your tumor based on its features. A final diagnosis is usually made based on these findings.

The pathology report is compiled by a pathologist, a doctor with specialized training in determining the nature and cause of disease. The pathologist conducts an examination of cells or tissue samples obtained during biopsy of the tumor or of the entire tumor after definitive surgery (removal of the tumor). The specimen is examined with and without a microscope, and its size, shape and appearance are documented and special tests may be performed. Cerebrospinal fluid (fluid around the brain and spinal cord) also may be collected for examination to help determine the grade of cancer by looking for the presence of tumor cells.

A neuropathologist, a pathologist who specializes in the examination and diagnosis of diseases of the brain and central nervous system, may also contribute by examining the tumor sample to determine the specific tumor type, test for tumor markers (biomarkers) and genetic abnormalities, and classify the tumor according to a grading system.

Classifying and Grading Brain Tumors

Brain and spinal cord tumors are given a grade based on how the tumor cells look and behave under a microscope. A tumor grade is different from the stage of a cancer. Cancer staging is based upon the size of a primary tumor and the location of cancer cells in the body. A tumor grade indicates how closely cancer cells resemble normal healthy cells. Cancer cells that resemble normal cells are called “well-differentiated,” and they grow and spread at a slower rate than “undifferentiated” and “poorly differentiated” cells, which look very abnormal when compared to normal cells. In some cases, a single tumor may consist of several different cell types. The tumor is graded overall based on the highest grade cells within the tumor.

The most commonly used grading system for brain tumors is the World Health Organization (WHO) Classification and Grading system for central nervous system tumors. This grading system helps doctors develop an appropriate treatment plan.

Brain Tumor Grades

Grade Description
Grade I The slowest growing and least malignant (cancerous) tumors, these tumors are often referred to as nonmalignant tumors. They consist of cells that look mostly normal when examined with the use of a microscope. These tumors rarely recur (come back) as a higher grade tumor.
Grade II These tumors grow relatively slowly and consist of cells that look only slightly abnormal when examined with the use of a microscope. They can spread into nearby normal tissue and may recur later as a higher grade tumor.
Grade III These malignant tumors quickly reproduce abnormal cells that are likely to spread to nearby normal tissue. They have a higher risk of recurrence and may return as a higher grade tumor. It can sometimes be difficult to differentiate between Grade II and Grade III tumors.
Grade IV The most rapidly growing type of brain tumor, these malignant tumors reproduce cells that appear completely abnormal and can easily spread into surrounding tissue.
Source: World Health Organization (WHO) Classification and Grading System (2017)

Other Brain Tumors

The four-grade classification system is used for many brain tumor types, but others, such as germ cell tumors and medulloblastomas, are classified using different methods.

Germ cell tumors are typically evaluated using magnetic resonance imaging (MRI) and tests done on cerebrospinal fluid because there is no universally accepted system to classify them. In general, doctors classify a germ cell tumor into one of two groups: M0 (metastatic-negative) or M+ (metastatic-positive).

Instead of using a classification system to determine a treatment plan for medulloblastomas, doctors develop a treatment plan based on factors that indicate the risk of tumor recurrence (returning after treatment). In general, doctors may classify medulloblastomas in children into one of two risk groups depending on the child’s age, how much of the tumor remains after surgery and whether the tumor has spread

  • Standard-risk: A standard or “average-risk” tumor is located in the very back portion of the brain and has not spread to other areas of the brain and spinal cord. This classification is assigned when almost all of the tumor is removed during surgery.
  • High-risk: A high-risk tumor has either spread to other parts of the brain or the spine, or has not spread, but more than 1.5 cc of the tumor remains after surgery. A high-risk classification may also be assigned to a tumor that initially appears to be a standard-risk tumor after biomarker testing is completed.

 

 

Additional Resources

 

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