Staging

Staging is a way of describing a tumor, such as where it is located, if or where it has spread, and if it is affecting the functions of other organs in the body. After a brain tumor has been diagnosed, additional tests will be done to learn more about the tumor.

There is no formal staging system for adult brain tumors. Instead, once a brain tumor has been diagnosed, the pathologist will perform several tests on a tissue sample of the tumor to learn as much as possible about the tumor. If the tumor is a glial brain tumor, the pathologist will assign a “grade” using a number from I to IV (one to four). The grade number indicates the degree of abnormality of the tumor cells. The degree of malignancy is often determined by characteristics of the tumor, as seen under the microscope. Generally, the lower the grade, the better the prognosis (chance of recovery or long-term control of the tumor).

There are several other factors that help doctors determine the appropriate brain tumor treatment plan and determine prognosis:

Tumor histology. As outlined under Diagnosis, a sample of the tumor is removed for analysis. How a tumor looks under a microscope is called tumor histology.

Normal brain tissue usually has differentiated tissue (different types of cells grouped together). Brain tissue that is cancerous is usually made up of cells that look more alike. In general, the more differentiated the brain tissue (and the lower the grade), the better the prognosis.

To determine histology of a tumor, doctors look at several factors including, but not limited to, the following:

• Mitosis (the number of cells dividing)
  
  
• Hypercellularity (if the tumor contains large numbers of cells)
  
  
• Vascular proliferation (if blood vessels in the tumor are growing)
  
  
• Necrosis (if there is any dead tissue in the tumor)

The pathologist can determine the type of tumor and its grade. To decide on the best treatment for a brain tumor, both the type and grade of the tumor must be established. In general, a tumor is referred to by grade. The higher the grade, the more rapidly growing the tumor is.

Specifically for astrocytoma, the grade is determined by its features, as seen under a microscope, according to the following criteria:

• Grade I represents a separate group of tumors. It refers to a juvenile pilocytic astrocytoma (JPA). The term juvenile does not refer to the age of the patient, but rather the type of cell. This is a benign, slow-growing tumor that can typically be cured with surgery. It is different from a low-grade astrocytoma or Grade II glioma, which have a high probability of a recurrence.
  
  
• A grade II tumor does not have mitosis, vascular proliferation, or necrosis, but exhibits increased cellularity.
  
  
• A grade III tumor is hypercellular and has mitosis but no vascular proliferation and no necrosis.
  
  
• A grade IV tumor has vascular proliferation and/or necrosis in addition to the factors common to grade II and III tumors.

Age of patient. In adults, the age of the patient (as well as his or her level of functioning, called functional status) at the time of diagnosis is one of the most significant predictors of outcome. In general, the younger the adult, the better the prognosis.

Extent of tumor residual. Resection is surgery to remove a tumor, and residual refers to how much of the tumor remains in the body after surgery. Four classifications are used:

• Gross total: The entire tumor was removed (microscopic cells may remain).
  
  
• Subtotal: Large portions of the tumor were removed.
  
  
• Partial: Only part of the tumor was removed.
  
  
• Biopsy only: Only a small portion, used for a biopsy, was removed.

Prognosis is most favorable when all of the tumor can be surgically removed.

Tumor location. A tumor can form in any part of the brain. Some tumor locations cause greater damage than others, and some tumors are harder to treat due to their location than others.

Functional neurologic status. The doctor will test how well a patient is able to function and carry out normal activities by using a functional assessment scale, such as the Karnofsky Performance Scale (KPS), outlined below.A higher score indicates a better functional status. Typically, the better someone is able to walk and care for themselves indicates a better prognosis.

100 Normal, no complaints, no evidence of disease

90 Able to carry on normal activity; minor symptoms of disease

80 Normal activity with effort; some symptoms of disease

70 Cares for self; unable to carry on normal activity or active work

60 Requires occasional assistance but is able to care for needs

50 Requires considerable assistance and frequent medical care

40 Disabled: requires special care and assistance

30 Severely disabled; hospitalization is indicated, but death not imminent

20 Very sick, hospitalization necessary; active treatment necessary

10 Moribund, fatal processes progressing rapidly

 0  Dead

Metastatic spread. A tumor that starts in the brain or spinal cord, if cancerous, often spreads within the CNS only and rarely metastasizes to other parts of the body in adults. For that reason, with few exceptions, tests looking at the other organs of the body are typically not needed.

Biogenetic markers. Certain molecular markers found in the tumor tissue can provide information on the tumor’s response to treatment. For instance, for oligodendroglioma, the loss of part of chromosome 1 on the p part of the chromosome, and the loss of part of chromosome 19 on the q part of the chromosome (called 1p and 19q) is associated with a much better response to chemotherapy and more successful treatment. Also, in glioblastoma, the modification of a gene called MGMT appears to be associated with improved responsiveness to treatment and better prognosis, but this is being tested in clinical trials (research studies).

Currently, the factors listed above are the best indicators of a patient’s prognosis. As discussed in Diagnosis, researchers are currently looking for tumor markers in the tumor tissue that could make a brain tumor easier to diagnose and the staging of an adult brain tumor possible in the future. These tools may someday make it possible for doctors to analyze the growth potential of brain tumors, develop more effective treatments, and more accurately predict prognosis.

Used with permission of the American Joint Committee on Cancer (AJCC), Chicago, Illinois. The original source for this material is the AJCC Cancer Staging Manual, Sixth Edition (2002) published by Springer-Verlag New York, www.cancerstaging.net.