This article will help you read and understand your pathology report for glioblastoma.
by Jane Barron, MD FRCPC, reviewed and updated on January 15, 2019
The brain is an organ that is found within the skull. It is part of a system known as the central nervous system which includes the brain and spinal cord. The brain is divided into the cerebrum, cerebellum, and brainstem. The spinal cord is a long thin structure that sits in the spinal column at the back of the body. The spinal cord starts in the neck and ends in the lower back.
The brain and spinal cord are made up of specialized cells called glial cells and neurons. The glial cells are further divided into cells called astrocytes, oligodendrocytes, ependymal cells, and microglial.
Glioblastoma is a cancer made up of abnormal astrocytes. Glioblastoma is the most common astrocytic derived tumor and the most common brain tumor found in adults. It can occur at any age, including childhood.
A biopsy is a surgical procedure that removes a small piece of tissue for examination by a pathologist. The purpose of a biopsy is to establish a diagnosis. A test called immunohistochemistry may be performed to confirm the diagnosis.
Tests results for isocitrate dehydrogenase (IDH) and O6-Methylguanine-DNA Methyltransferase (MGMT) methylation may also be included in your biopsy report.
Your doctors will use this information to plan treatment such as surgery, radiation, and chemotherapy. Continue reading to learn more about the information found in this report.
After the tumour has been removed completely, it will be sent to a pathologist who will prepare another pathology report. This report will confirm or revise the original diagnosis. If additional immunohistochemical or molecular tests are performed, the results will be described in this report.
Pathologists use the word grade to describe how different the cancer cells in glioblastoma look compared the cells normally found in the brain or spinal cord.
Brain and spinal cord tumors are given a World Health Organization grade of I to IV. For glioblastoma, the grade can only be determined after your pathologist has examined the tissue under the microscope.
Your pathologist will look for the following features in order to determine the grade:
Why is this important? Grade is important, as the higher grade tumors, grade III and IV, have a worse prognosis compared to the lower grades. Glioblastoma is a World Health Organization (WHO) grade IV tumor.
Your pathologist may perform a test called immunohistochemistry which allows your pathologist to see the proteins being made by the tumour cells. If the tumour cells are making a protein, the result will be described as positive or reactive.
The results can be variable for each marker but usually glioblastoma tumour cells are usually positive for glial fibrillary acidic protein (GFAP), S100, vimentin, and p53.
Isocitrate dehydrogenase (IDH) is a special protein that can be found inside glioblastoma tumour cells. There are two forms of the IDH protein made by the genes IDH1 and IDH2.
A genetic alteration, called a mutation, can occur in either of these genes which causes the cell to produce an abnormal IDH protein.
Why is this important? A glioblastoma that has a mutation in IDH1 or IDH2 (a mutant glioblastoma) is associated with a better prognosis compared to a glioblastoma that does not possess a mutation (IDH-wildtype).
MGMT is a special protein found in all cells. In some glioblastomas, the MGMT protein can undergo a change, called methylation. This change causes the tumour cell to produce less MGMT protein.
Why is this important? Your pathologist can perform a test to see if the MGMT in your tumour shows methylation. If testing shows that a glioblastoma is methylated it could be associated with a better response to certain chemotherapy drugs compared to a tumor that is not methylated.