Brain Tumors

Pathology and Grading

Results from tests to diagnose your tumor are summarized in a pathology report, and your final diagnosis is usually based on these findings. This essential information becomes a roadmap to guide your medical team in planning the most effective course of treatment based on your tumor’s specific characteristics.

The report is compiled by a pathologist, a doctor with specialized training in studying cells or tissue under a microscope, to determine the nature and cause of diseases. The pathologist examines the biopsied tissue or cells, documenting the cells’ size, shape and appearance, and may perform tests. In some cases, the entire tumor is examined after it is removed by surgery. Cerebrospinal fluid, found in and around the brain and spinal cord, may be collected to help determine the tumor’s grade by examining it for the presence of any tumor cells.

A neuropathologist, who specializes in diagnosing diseases of the central nervous system, may contribute to the report. He or she will examine the specimen to determine the specific tumor type and test for biomarkers and genetic abnormalities (see Diagnosing and Biomarkers). The tumor is then classified according to the system/method typically used for its specific type.

Grading Brain Tumors

Most types of brain and spinal cord tumors, including gliomas and meningiomas, are classified by grades, which are different from the stages used to classify most other cancers. Tumor grades are based on how closely the cells resemble normal, healthy cells when viewed under a microscope.

Brain tumors are most commonly graded using the World Health Organization (WHO) Classification and Grading System for central nervous system tumors. It ranges from Grade I, indicating slow-growing nonmalignant (noncancerous) tumors, to Grade IV, for rapidly-growing malignant tumors that can spread into surrounding tissue.

Tumor cells resembling normal cells are called well-differentiated. They grow and spread at a slower rate than undifferentiated or poorly differentiated cells, which look very abnormal in comparison. A tumor may sometimes contain different grades of cells, in which case the tumor’s overall grade will be based on the highest-grade cells.

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)

Classifying Other Types of Tumors

Some types of brain tumors, such as germ cell tumors and medulloblastomas, are classified using other methods.

There is no universally accepted system for classifying germ cell tumors, so they are typically evaluated by magnetic resonance imaging (MRI) and tests on cerebrospinal fluid. In general, doctors classify germ cell tumors in adolescents and young adults as either M0 (metastatic-negative) or M+ (metastatic-positive).

For medulloblastomas, doctors base treatment on factors indicating the risk of tumor recurrence (returning after treatment) rather than on a classification system. In general, doctors 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 it has spread.

  1. Standard-risk: A standard- or average-risk tumor is in the very back portion of the brain and hasn’t spread to other parts of the brain or spine. This classification is assigned when nearly all of the tumor is removed during surgery.
  2. High-risk: A high-risk tumor may or may not have spread, but more than 1.5 cc of the tumor remains after surgery. A tumor that initially appears to be standard-risk may be given a high-risk classification after biomarker testing is completed.

Ask your doctor to go over your pathology report with you, and request a copy. Understanding these findings will help you as you and your medical team make shared treatment decisions, including evaluating clinical trials.

 

Additional Resources

 

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