What are the different types of gliomas?

While there are many different types of cancers, all cancers begin in approximately the same way—normal cells undergo genetic mutations or other changes, creating cancerous cells that grow in an uncontrolled way. Cancerous cells can form tumors, invade nearby tissues, spread to other parts of the body, and disrupt the normal functioning of the organs and systems they come into contact with.

Gliomas are a group of cancers that originate in the central nervous system. Most gliomas originate in the brain, but some originate in the spinal cord. While there are different types of gliomas, all gliomas begin with mutations to glial cells.

What are glial cells?

Glial cells make up the tissues that surround, support, and protect nerves. They are abundant in the central nervous system, but also found in the peripheral nervous system (the parts of the nervous system located outside of the brain and spinal cord).

There are several different types of glial cells and there are different types of gliomas. Identifying the type of glioma is an important step in diagnosis, as some types are more aggressive that others, and are more likely to grow quickly, invade nearby tissues, and spread to distant sites in the body.

What are the different types of gliomas?

The classification of gliomas has been updated several times in the past decades. In 2021, the World Health Organization (WHO) updated the classification of gliomas, with separate classifications for adult and pediatric gliomas.

Pediatric gliomas are categorized as low-grade or high-grade. Grade refers to how abnormal the cancer cells look and behave compared to normal cells. Grading is done on a scale of I to IV.

• Low-grade gliomas refer to grades I and II. Low-grade gliomas are less likely to grow quickly and spread aggressively.
• High-grade gliomas refer to grades III and IV. High grade gliomas are more likely to grow quickly and spread aggressively.

These updates classify adult gliomas based on the presence of specific genetic mutations and molecular characteristics. There are three main types:

Astrocytoma, isocitrate dehydrogenase (IDH)-mutant

• Astrocytoma refers to a cancer that originates from glial cells called astrocytes.
• Isocitrate dehydrogenase (IDH) is an enzyme (a substance that speeds up a chemical process). IDH plays an essential role in cellular metabolism, the chemical processes that occur at the cellular level.
• IDH-mutant means that the cancer cells have a mutated version of the gene that contains instructions for making IDH enzyme, which the cancer uses to promote its growth and spread.
• Some anti-cancer drugs—called targeted therapies—work by blocking IDH, helping to slow the growth of the cancer.

Oligodendroglioma, IDH-mutant, and 1p/19q-codeleted

• Oligodendroglioma refers to cancer that has originated in glial cells called oligodendrocytes.
• This type of glioma also has mutations to the IDH gene.
• 1p/19q-codeletion refers to changes in the chromosomes of the cancerous cells. Chromosomes are packages of DNA found in a part of a cell called the nucleus. Chromosomes help cells store DNA and keep DNA intact as cells divide and new cells are produced. Oligodendroglioma cells are missing pieces of two chromosomes, numbered 1 and 19.

Glioblastoma, IDH-wildtype

• Glioblastoma (GBM) type also originates from astrocytes.
• It is the most aggressive form of glioma and is given the highest grade, grade IV. Glioblastomas grow and spread quickly and contain cancerous cells that are highly abnormal.
• IDH-wildtype means that there are no mutations to the IDH gene, though there may be other mutations and alterations to chromosomes.
• This type of glioma often contains blood vessels (which are used to fuel growth) and areas of dead cells (called necrosis, which is associated with more aggressive growth). These features can be present in other gliomas as well.

As the above illustrates, gliomas are complex conditions, and a diagnosis may include a number of clinical terms. While these terms point toward important information that can help guide treatment of the glioma, it can also feel overwhelming. If you have questions about a diagnosis, your best source of answers will be your healthcare team.