Diagnosing and Biomarkers
Determining your best treatment options begins with learning the location and size of the brain tumor. Several diagnostic tests may be performed along with a physical and neurological exam, including imaging tests and a biopsy. Your doctor may include any of the following tests to diagnose your tumor and begin planning your treatment.
Angiogram uses X-rays and contrast injected into your arteries and/or veins to identify the network of blood vessels that supply the tumor.
Computed tomography (CT) produces three-dimensional, cross-sectional X-ray images. It may be used to measure the tumor’s size, look for changes to the skull and find bleeding or enlarged ventricles.
Electroencephalography (EEG) is a non-invasive test to measure and record the electrical activity that is produced when brain cells communicate with each other. Special sensors, called electrodes, are attached to the outside of your head and are connected to a computer that displays the activity in wavy lines.
Hemodynamic imaging measures the brain’s blood flow and supply. The photos taken are used to create images of the blood flow into the tumor, allowing the doctor to see the tumor’s blood supply.
Magnetic resonance imaging (MRI) uses magnetic fields to create visual images of internal structures of the body. Multiple types of MRI exist and function differently, including functional MRI (fMRI), flow-sensitive MRI (FS MRI), dynamic MRI (also called perfusion MRI), diffusion weighted imaging and spinal MRI.
Magnetic resonance spectroscopy (MRS) measures metabolites (substances produced by living tissue) to create images that represent patterns of activity in the brain. These patterns can be helpful in diagnosing specific types of brain tumors or to help determine whether a tumor is malignant.
Positron emission tomography (PET) images are not as finely detailed as those from CT or MRI but can provide helpful information to supplement those results and determine tumor grade. This test may be used to determine if the tumor is primary or a metastasis from elsewhere in the body.
Single photon emission computed tomography (SPECT) is similar to PET but uses a special camera to detect radioactive material that has been injected into the body. It is rarely used to diagnose brain tumors but may help the doctor distinguish between low- and high-grade tumors.
Lumbar Puncture (Spinal Tap)
A spinal tap is used to collect a sample of cerebrospinal fluid, which is examined for the presence of tumor cells, blood infection and proteins. This procedure may be used to help diagnose pineal region or meningeal tumors or central nervous system lymphoma, as well as tumors that have spread after surgery.
A biopsy is the removal of tissue from a suspected tumor or removal of the entire tumor during surgery. Three types are generally used for brain tumors: needle biopsy, open biopsy and stereotactic biopsy. Your pathologist may perform biomarker testing on the tissue sample to provide more information about the type of brain tumor.
Biomarkers: Research Uncovers Genetic Information About Brain Tumors
Doctors now understand that genetic mutations are involved with some brain tumors. These mutations can be detected through molecular testing of the tumor or a sample of its tissue, which shows the unique DNA of the tumor. Your doctor may also order genetic testing from a blood sample to examine your individual genetic material for any mutations.
Biomarkers are substances produced by cancer cells or other cells in the body in response to cancer. These can include specific genes, proteins or molecules of the tumor and can be measured in the blood, plasma, urine, cerebrospinal fluid or other body fluids or tissue.
Pathologists, who have special training in identifying cells and tissues under a microscope, look for specific biomarkers in the sample. While examining a sample for biomarkers, the pathologist will look for certain genetic abnormalities, including chromosomes that change places to extra copies of a gene and mutations (any change in the DNA sequence of a cell).
Doctors use biomarkers to determine a prognosis (outlook), to predict how the person will respond to treatment or to diagnose a tumor. A prognostic biomarker provides information about a person’s overall cancer outcome, regardless of therapy, while a predictive biomarker gives information about the effect of a specific treatment approach. Diagnostic biomarkers help determine the type of tumor. Some biomarkers may also help determine how aggressive (fast growing) a tumor is and may predict long-term survival.
Following are the most commonly tested biomarkers in people with brain tumors:
- 1p/19q co-deletion. Genetic changes in chromosomes 1 and 19 can occur in tumor cells (primarily for oligodendrogliomas and anaplastic oligodendrogliomas). The test for this is prognostic, predictive and diagnostic.
- Isocitrate dehydrogenase (IDH-1). This mutated gene may be found in low-grade tumors, specifically oligodendrogliomas, astrocytomas and secondary glioblastomas. The test for this is prognostic and diagnostic.
- Methyl guanine methyl transferase (MGMT). This is a gene involved with DNA repair. The test is most commonly used with glioblastomas and is prognostic and predictive.
Although testing for brain tumor biomarkers is still new and mostly performed in clinical trials, it is becoming more a part of regular clinical practice. Finding new biomarkers may help doctors diagnose brain tumors earlier or direct treatment options. In addition, knowing your biomarkers may help determine eligibility for clinical trials. Ask your doctor if biomarker testing is right for you.