Brain Tumors

Pathology & Grading 

A pathology report is an essential document that provides information about the specific characteristics of your tumor. It serves as a guide for your health care team to plan the treatment most likely to be effective for your tumor based on its features.

Most often, a diagnosis is made after careful examination of a biopsy tissue sample from a suspected tumor, or of the entire tumor after definitive surgery (removal of the tumor). A pathology report is prepared by a pathologist, who is a doctor with specialized training in determining the nature and cause of disease. The pathologist examines the sample with and without a microscope, documenting its size, describing its appearance and, sometimes, performing special testing. The final diagnosis is based on all the findings of the examination.

Diagnosing a brain tumor and identifying all of the characteristics of the tumor are challenging and require the expertise of physician specialists. A neuropathologist specializes in diseases of the central nervous system, which includes the brain and spinal cord. The neuropathologist will examine 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. Treatment is planned according to the final results of the pathology report.

Classifying and Grading Brain Tumors

Depending on the diagnosis, doctors usually need to determine the grade of the brain tumor. Brain and spinal cord tumors are given a grade according to how the tumor cells behave and look under the microscope. The most commonly used grading system for brain tumors is the World Health Organization (WHO) Classification and Grading system for central nervous system tumors.

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.

General brain tumor grades

In general, your doctor may classify your brain tumor into one of four grades.

  • Grade I tumors are the slowest growing and least malignant (cancerous) tumors, and 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 tumors are relatively slow-growing 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 tumors are considered malignant, with abnormal cells that reproduce quickly and are likely to invade 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 tumors are rapidly growing, malignant tumors with cells that appear completely abnormal and can easily spread into surrounding tissue.

Other brain tumors

Although many brain tumors are classified as one of four grades, other tumor types, including germ cell tumors and medulloblastomas, use a different classification method.

Although no universally accepted system exists for germ cell tumors of the brain, doctors traditionally evaluate them with the use of magnetic resonance imaging (MRI) and tests done on cerebrospinal fluid. 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 a medulloblastoma, doctors develop a treatment plan based on factors that indicate the risk of tumor recurrence (returning after treatment). In general, doctors may classify a medulloblastoma in children into one of two 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 remain after surgery. A high-risk classification also may be assigned to a tumor that initially appears to be a standard-risk tumor after biomarker testing is completed.


The Importance of a Second Opinion

Getting a second opinion is common, particularly when dealing with a complex health condition such as a brain tumor. Different specialists offer various levels of expertise and experience, and they may favor a different approach. Another specialist may share information your first doctor didn’t mention, such as available clinical trials or how a treatment may affect your quality of life.

Getting a second opinion from another pathologist or neurologist with extensive expertise in interpreting pathologic findings related to brain tumors can be beneficial, especially if there was difficulty or controversy in interpreting the findings. Be sure to ask your doctor to seek a second opinion if the pathology report does not contain a definitive diagnosis or if you have a rare type of tumor. Another interpretation can confirm the findings or may suggest an alternative diagnosis.

It’s important to remember that you’re not second-guessing your doctor by seeking a second opinion. You’re advocating for the best care possible. Most doctors support their patients seeking another professional opinion, and many will offer a referral to another specialist.

Although a brain tumor diagnosis can be overwhelming, it is important to obtain all of the information about your tumor before deciding which treatment options are right for you. Regardless of the choice you make, you can take comfort in knowing you explored your options.



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