Gliomas

ALSO KNOWN AS: Malignant gliomas, brain tumors, astrocytomas, ependymomas, glioblastomas, oligodendrogliomas

RELATED CONDITIONS: Central nervous system tumors, primary brain tumors

DEFINITION: A glioma is a brain tumor that develops from a neuroglia, commonly known as a glial cell. Glial cells are support cells for the neurons that send and receive signals in the nervous system. Some of the main types of glial cells that can grow into gliomas are: microglia, astrocytes, oligodendrocytes, and ependymal, Schwann, and satellite cells. Gliomas are categorized and named based on their glial cell of origin, are considered primary central nervous system tumors, and occur in both children and adults. A glioma is a primary brain tumor, meaning that the tumor started in the brain.

An astrocytoma is the most common glioma and occurs in children and adults. Brain stem gliomas form at the connection between the brain and the spinal cord and are most common in children between the ages of three and ten but do occur in adults. Glioblastoma multiformae (more commonly called simply "glioblastoma") is the most aggressive of gliomas. All told, gliomas account for about 33 percent of all brain and central nervous system cancers in children and between 75 and 78 percent of all brain tumors in adults.

Risk factors: Most brain tumors have no known risk factors. Exposure to radiation or radiation of the brain may cause a brain tumor. There are no studies that prove brain tumors are caused by cell phone use, electric lines, injury or accidents, exposure to toxic fumes, hair dyes, or any food or food product. The National Cancer Institute reports that exposure to vinyl chloride, a gas used in making plastic, may increase the chance of developing glioma.

Etiology and the disease process: There is no known cause for glioma. Malignant gliomas are aggressive tumors that may spread quickly throughout the brain. Because the brain controls almost all body functions, a rapidly growing tumor may cause problems with breathing, sight, hearing, smell, balance, body temperature, and other functions, creating life-threatening conditions. As the glioma increases in size, the symptoms progress, leading to difficulty with activities of daily living.

Incidence: Gliomas account for approximately 33 percent of all brain tumors and 78 percent of all malignant brain tumors. According to the American Cancer Society's estimates for 2023, nearly 25,400 brain and spinal cord cancers are diagnosed each year in the United States, of which more than 4,000 are found in children and adolescents. An estimated 300 to 400 brain stem cancers, including diffuse astrocytomas and pilocytic astrocytomas, are diagnosed in American children each year, according to the National Cancer Institute.

Symptoms: Depending on the type and grade of the tumor, tumors may grow one to two years before symptoms develop. The brain can adjust to a slow-growing, low-grade tumor and may adapt over time, but symptoms eventually will occur. A high-grade or aggressive tumor may cause dramatic symptoms that develop quickly. The most common symptoms are headache, seizures or convulsions, weakness or paralysis, nausea or vomiting, difficulty walking due to poor balance, behavior changes, confusion, and vision changes.

Screening and diagnosis: There are no screening tests for gliomas, although molecular markers have been increasingly deployed by doctors in the 2020s. Diagnosis begins when the patient complains of symptoms suggestive of a glioma. A physician specializing in neurology or neurosurgery should be involved in a comprehensive physical examination of the patient. Diagnostic imaging tests such as computed (CT) and (MRI) of the head are most commonly used when a patient exhibits symptoms. A positron emission tomography (PET) scan may be used to determine if the tumor is malignant. A is generally not done for diagnosis because of the inability to reach the tumor, but one is usually done at the time of surgery to determine the specific cell type. Staging is based on identifying the location of the (T X-4), evidence of metastasis (M X-1), and grade (G I-IV).

Treatment and therapy: Treatment for gliomas is difficult and usually combines surgery (if the tumor can be reached) and radiation. Radiosurgery is an option if the tumor is inoperable. Chemotherapy has limited use because of the difficulty of getting the drugs into the brain in the proper amounts to kill cells. Carmustine (BCNU) is one drug that can penetrate the brain and has shown some activity against gliomas. It does have toxicity that limits its use. Vorasidenib, a targeted drug for IDH1/2 mutant gliomas, has also shown promise, along with CAR-T cell therapy and immunotherapy. Treatment recommendations are consistently moving toward surgery, radiation, and systemic chemotherapy. Advances in the treatment of gliomas include a wafer with carmustine placed into the surgical site after tumor removal. Temozolomide (Temodar), an oral drug with few side effects, has shown activity when a glioma returns. Clinical studies are ongoing to determine other chemotherapy combinations useful in treating gliomas. Combination therapies and targeted treatment plans are increasingly used to enhance the effectiveness of treatments.

Prognosis, prevention, and outcomes: The prognosis depends on the type of glioma, the patient's age, and the patient's symptoms when diagnosed. Gliomas are challenging to treat, and survival time is often limited. Five-year survival rates for childhood gliomas range from less than 10 percent to over 90 percent, depending on the type of tumor. Survival rates for adult gliomas range from 5 to 95 percent, depending on tumor type and patient age. Slower-growing, low-grade tumors, even when treated successfully at first, have the potential to grow back and progress. Avoiding radiation to the head is the only documented prevention. If the tumor is treated successfully, which is rare, there may still be significant physical limitations that exist from the side effects of the tumor or its treatment. 

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