© 2005-2012 American Society of Clinical Oncology (ASCO). All rights reserved worldwide.
Staging is a way of describing where the tumor is located, if or where it has spread, and whether it is affecting the functions of other organs in the body. A staging system is used for most other types of cancer. There is a formal staging system for adult brain tumors; however, the grading system described below is always used instead.
After a brain tumor has been diagnosed, additional tests will be done to learn more 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 indicates how different the tumor cells are from healthy cells, with a higher grade tumor having cells that are the least like healthy cells. The characteristics of the tumor, as seen under the microscope, help determine how cancerous a tumor is. 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 glial 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 determined. In general, a tumor is referred to by grade. The higher the grade, the more rapidly growing the tumor is.
Specifically for glial tumors, the grade is determined by its features, as seen under a microscope, according to the following criteria:
- Grade I is a separate group of tumors called 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 noncancerous, slow-growing tumor that can typically be cured with surgery. It is different from a low-grade astrocytoma or Grade II glioma, which are likely to recur.
- A grade II tumor does not have mitosis, vascular proliferation, or necrosis, but shows increased cellularity.
- A grade III tumor is hypercellular and has mitosis but no vascular proliferation and no necrosis. It is often called anaplastic astrocytoma
- A grade IV tumor (glioblastoma, also called glioblastoma multiforme or GBM) 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, see below) when diagnosed is one of the best ways to predict a patient's prognosis. In general, a younger adult has a better 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.
A patient's prognosis is better 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 more damage than others, and some tumors are harder to treat because of their location.
Functional neurologic status. The doctor will test how well a patient is able to function and carry out everyday 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
Metastatic spread. A tumor that starts in the brain or spinal cord, if cancerous, often spreads within the CNS only and rarely spreads 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. A tumor that does spread to other parts of the brain or spinal cord is associated with a poorer prognosis.
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 a 1p and 19q co-deletion) is associated with a much better response to chemotherapy and more successful treatment and can be used to help plan treatment, especially for anaplastic oligodendroglioma. Also, in glioblastoma, whether a gene called MGMT is changed can help understand a patient's prognosis, and it is being tested in clinical trials (research studies).
Recurrent tumor. A recurrent tumor is one that comes back after treatment. If there is a recurrence, the tumor may need to be graded again using the system above.
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 help doctors analyze the possibility that a brain tumor will grow, 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, Seventh Edition (2010)published by Springer-Verlag New York, www.cancerstaging.net.