Is Glioma Cancerous?

• What is cancer?
• Glioma tumor grading
• Are low-grade gliomas cancerous?
• Are high-grade gliomas cancerous?

Gliomas are the most common type of primary brain tumor, accounting for about a third of all cases. They can be noncancerous (benign) or cancerous (malignant) and can cause a variety of symptoms depending on the location and size of the tumor. Treatment options vary depending on the location, stage and grade of the tumor but may include surgery, radiation therapy, and chemotherapy.

Cancerous cells are cells that divide without proper regulation and do not act like normal cells in their environment. Normal tissues usually grow in pre-established patterns and respect certain boundaries. Cancerous tissue has broken away from this pattern and can grow in much more unpredictable ways, such as reproducing much faster than normal cells and therefore interfering with function of the surrounding normal tissues. 

Tumor grading is the process of determining the severity of cancer. This is done by examining the tumor tissue under a microscope and assigning it a grade (typically from 1 to 4). Grades 1 and 2 are considered low-grade tumors, while grades 3 and 4 are high-grade tumors. The higher the grade, the more aggressive the tumor is and the less likely it is to respond to treatment. Low-grade tumors are less aggressive and tend to grow more slowly than high-grade tumors. They may even not require treatment right away in select cases, but they should be monitored closely. High-grade tumors are more aggressive and can grow quickly.

Low-grade gliomas are generally considered to be noncancerous but this is a relative definition. They grow slowly and typically have a good prognosis. However, many low-grade tumors cannot be removed completely via surgery and the residual tumor can become cancerous with time. Therefore, the benign versus malignant separation has gray zones and is not always as clear cut as patients might expect.

Noncancerous tumors are generally benign, meaning they do not spread to other parts of the body. Although noncancerous brain tumors may grow slowly, they often press on healthy brain tissues and can sometimes cause life-threatening problems.

The most common types of low-grade gliomas are:

• Oligodendroglioma: This type of tumor occurs from the cells that surround the nerve fibers in the brain and is usually found in the frontal or parietal lobes. Oligodendrogliomas are low-grade tumors and may be treated with surgery and radiation therapy.
• Astrocytoma: This type of tumor occurs from the cells that support the nerve cells in the brain and usually is found in the cerebrum or spinal cord. Astrocytomas are low-grade tumors but can sometimes become more aggressive over time. For instance, a glioblastoma is a type of astrocytoma, but the most aggressive type (Grade IV). Treatment options vary depending on the stage and grade of the tumor but may include surgery, radiation therapy, and chemotherapy.
• Oligoastrocytoma: This type of tumor is a combination of oligodendroglioma and astrocytoma cells and is usually found in the cerebrum. Oligoastrocytomas are low-grade tumors and can usually be treated with surgery and radiation therapy.
• Meningioma: This tumor develops from the meninges (the membranes that surround the brain) and is usually benign. Surgical removal of the tumor may result in a full recovery and long lifespan.
• Choroid plexus papilloma: This type of tumor develops from the cells that produce cerebrospinal fluid and is typically found in infants or young children. Surgery can remove this type of tumor, which is rarely cancerous.

High-grade gliomas are much more invasive and are generally considered cancerous. They grow rapidly and typically have a poor prognosis. The most common types of high-grade gliomas are:

• Glioblastoma: This type of tumor is usually found in the cerebrum. Glioblastomas are high-grade tumors and are usually treated with combinations of surgery, radiation therapy, and chemotherapy.
• Anaplastic astrocytoma: This type of tumor is usually found in the cerebrum or spinal cord. Anaplastic astrocytomas are high-grade tumors and have a poor prognosis. Surgery, radiation therapy, and chemotherapy may be used in combination to slow the growth of the tumor.

If you have been diagnosed with a glioma, it is important to know the exact type of tumor and how invasive it appears under the microscope (its official grade). It is also important to determine whether it has spread to other parts of the brain or body (metastasized). There are many treatment options available today which may help to slow down the growth and spread of the tumor over time; however, not all treatments are equally effective against all types of tumors.

• The benign versus cancerous delineation that applies to other tumor types elsewhere in the body may not apply to the tumors in the brain.
• Although grade I gliomas (such as pilocytic astrocytomas) do act benign, low-grade-gliomas (Grade II: astrocytomas, oligodendrogliomas, etc.) continue to grow slowly and can transform to cancerous tumors despite their surgical removal as surgery is not able to completely remove all gliomas. These tumors have finger-like projections that invade the normal brain, therefore preventing their safe and complete removal.
• Learning about how different kinds of brain tumors behave will give you peace of mind and inform your decisions during the treatment planning process.