Glioma is a broad category of brain and spinal cord tumors that come from glial cells – brain cells that support nerve cells.
The symptoms, prognosis, and treatment of a glioma depend on the person’s age, the tumor type and biomarkers, and the location of the tumor within the brain. Some of these tumors can grow fast or aggressively and get into normal brain tissue, which makes surgical removal very difficult – or sometimes impossible – and complicates treatment.
Glioblastomas are the most common cancerous brain tumors in adults. They're more common in older adults. Brain tumors are slightly more likely to happen in males.
Prior radiation to the brain is a risk factor for malignant glioblastomas and other high-grade gliomas. Head trauma is also a risk factor for these brain tumors. Some genetic disorders also increase the risk of children getting the tumors, but rarely in adults.
There are no lifestyle risk factors linked to malignant gliomas. This includes alcohol, cigarette smoking, or cellphone use.
Are There Different Types of Gliomas?
Gliomas are named based on the specific type of glioma, or brain cell, affected. They are also categorized by grade. Most often, they're "slow-growing" or "low-grade," and "high-grade" or "rapid-growing" tumors. Three of the most common types are:
Astrocytomas start in brain cells called astrocytes. Most of these brain tumors cannot be cured because they spread all through normal brain tissue. Astrocytomas are usually classified based on criteria used by a doctor examining the biopsy under a microscope. Tumors that are grade 1 grow the slowest, while grade 4 tumors, the highest grade, are the fastest growing.
Oligodendrogliomas start in cells called oligodendrocytes. These tumors spread kind of the way astrocytomas do. Some of these tumors may be slow-growing but still spread into nearby tissue. Sometimes they can be cured. A higher-grade oligodendroglioma grows and spreads more quickly and usually can’t be cured.
Glioblastomas are considered to be a separate type of glioma that begin very early in the development of glial cells, before they've become either astrocytes or oligodendrocytes. High-grade gliomas, like glioblastomas, are the most common type of malignant central nervous system tumors in adults and also the most aggressive.
What Are the Symptoms of a Glioma?
Symptoms of a glioma are like those of other malignant brain tumors and depend on the area of the brain affected. The most common symptom is a headache – affecting about half of all people with a brain tumor. Other symptoms can include seizures, memory loss, physical weakness, loss of muscle control, visual symptoms, language problems, a loss of thinking skills, and personality changes. These symptoms may change according to which part and how much of the brain is affected.
Symptoms may worsen or change as the tumor continues to grow and destroys brain cells, compresses parts of the brain, and causes swelling in the brain and pressure in the skull.
How Are Gliomas Diagnosed?
If a brain tumor is suspected, a brain scan is usually done. This includes a CT scan, an MRI scan (considered to be superior), or both. If the brain scan suggests a brain tumor, a biopsy may be performed for diagnosis. A biopsy may be done as a separate procedure or at the time the tumor is removed if surgery is a treatment option. When a biopsy is done separately either because you are too ill or the tumor is in a critical part of your brain, doctors can perform a procedure called a stereotactic needle biopsy. It is used to take a sample of the tumor. A small opening in the skull is made, then a needle is inserted through the opening to get tissue from the brain tumor.
How Are Gliomas Graded?
Gliomas have subtypes and are graded by numbers. The grade of a tumor is determined by how the cancer cells appear under a microscope and by the genetic profile of the tumor. Grade 1 tumors grow slowly and can sometimes be totally removed by surgery, while grade 4 tumors are fast-growing, aggressive, and hard to treat.
According to the current World Health Organization (WHO) system, gliomas are classified and graded as follows:
Astrocytomas
These tumors have a mutation in one of the IDH genes, which makes them respond better to certain types of treatment. Absence of what's called a TERT promoter mutation, coupled with IDH mutation and lack of 1p/19q codeletion, is a sign of an astrocytoma.
- Grade 1 gliomas include pilocytic astrocytomas and subependymal giant cell astrocytomas (SEGAs). They are more common in children.
- Grade 2 tumors are also called diffuse astrocytomas, which means they can spread into surrounding brain tissue.
- Grade 3 astrocytomas are also diffuse and faster-growing. They're considered high-grade.
- Grade 4 is the most aggressive type of astrocytoma. Cancer cells are missing the tumor-suppressing genes CDKN2A and CDKN2B.
Oligodendrogliomas
While these tumors also have an IDH mutation, they're identified by chromosome changes inside the cell DNA called 1p/19q co-deletion. Many also contain TERT promoter gene mutations that help them survive.
All oligodendrogliomas can spread. They are only grade 2 (slower growing) or grade 3 (faster growing).
Glioblastomas
These tumors are always grade 4. They do not have an IDH mutation, and they have several genetic features that help them stay alive, including TERT promoter and EGFR amplification gene mutations and an extra copy of chromosome 7 or a missing chromosome 10. That makes them very fast-growing and difficult to treat successfully.
About half of glioblastomas have a gene mutation called MGMT promoter methylation. This means that the cancer is more likely to respond to chemotherapy treatment.
Ependymomas
There are many subtypes of ependymomas, based on their location, cell features, and genetic traits. They include:
- Grade 1 tumors are the least aggressive and include subependymomas. These are more common in adults.
- Grade 2 tumors include myxopapillary ependymomas, which are more likely to come back after treatment, and other types of ependymomas with cells that look less like normal cells under a microscope.
- Grade 3 means the cells are even further from normal in appearance and the cancer is more likely to grow and spread. This can be applied to any type of ependymoma.
Some low-grade tumors can grow into high-grade tumors.
How Are Gliomas Treated?
Different treatment options are considered for high-grade malignant gliomas, depending on the location of the tumor, type of glioma (cell type), biomarkers, and grade of malignancy. The patient’s age and physical condition also play a role in determining treatment. Treatment for gliomas has many steps and may include:
Tumor removal by surgery. The patient should be otherwise relatively healthy. And they should be able to maintain their brain function, speech, and mobility. Imaging techniques such as cortical mapping and functional MRI may be used to help the surgeon remove the tumor. The goal is to take out as much of the tumor as possible, improve symptoms, delay progression, and improve survival without affecting important brain function. These tumors often come back. And all high-grade gliomas recur.
Radiation therapy uses high-energy X-rays or other radiation to kill cancer cells.
Chemotherapy uses drugs to stop the growth of cancer cells. This therapy may be taken by mouth or as an injection.
Targeted therapy is a newer type of treatment that may be used to help shrink tumors. It works differently from chemotherapy in that it targets certain proteins or specific biomarkers that help tumors grow. Biologics are targeted treatments made from living organisms.
Alternating electric-field therapy uses low-intensity energy to create electrical fields that target tumor cells while not hurting normal cells. It's done by putting electrodes directly on the scalp. The device is called Optune Gio. It's given with chemotherapy after surgery and radiation. The FDA has approved it for use in both newly diagnosed adults and adults whose glioblastoma has come back.
Supportive therapy to improve symptoms and neurologic function includes corticosteroids to reduce swelling in the brain caused by the tumor and anticonvulsants to control or prevent seizures.
Clinical trials, which are done to see if new cancer therapies work well and are safe, are another option.
Treatment for low-grade astrocytomas
The main treatment for low-grade astrocytomas is surgery. But because these tumors penetrate deep into the brain and grow into normal brain tissue, surgery is sometimes difficult. Radiation is often recommended after surgery or if there is a recurrence. Chemotherapy may also be used after surgery or as part of the treatment of recurrences. Targeted therapy may be used in some people.
Treatment for high-grade astrocytomas and glioblastomas
Treatment for high-grade astrocytomas or glioblastomas is surgery, if possible. After surgery, radiation therapy, along with chemotherapy, is the next step. Targeted therapy or biologics may be used in some people. Sometimes surgery to remove the high-grade tumor is not possible. Then radiation and chemotherapy are used. If the tumor returns or gets worse after chemo and radiation, targeted therapies and biologics can be used for IDH mutation-positive tumors. Surgery may be repeated along with other forms of systemic treatments (that go throughout your body). Clinical trials may also be recommended to allow patients to use new therapies.
Treatment for oligodendrogliomas
For oligodendrogliomas, surgery is the first choice of treatment to help relieve symptoms and increase patient survival. Radiation with or without chemotherapy may be given after surgery. Also, chemotherapy or radiation may be used to shrink a tumor before surgery. When radiation and chemotherapy can't be done, systemic treatments with a biologic that targets IDH mutations can be given.
Treatment for ependymomas
Ependymomas usually do not pass into normal brain tissue the way other gliomas do. So surgery may be highly effective if all of the tumor is removed. But ependymomas may seed the cerebrospinal fluid so the entire spinal canal needs evaluation with MRI scanning. These tumors are highly responsive to radiation.
What’s the Prognosis for People With Gliomas?
High-grade gliomas generally have a poor prognosis, especially for older patients. But tumor biomarkers can affect overall survival, progression-free survival, and can help with treatment decisions.
