Astrocytomas

ALSO KNOWN AS: Gliomas

RELATED CONDITIONS: Primary brain tumors

DEFINITION: Astrocytomas, the most common gliomas, are primary malignant brain tumors that can occur in most parts of the brain and occasionally in the spinal cord. As the name implies, astrocytomas are derived from astrocytes, which are nonneural support cells of the central nervous system. The types of astrocytomas based on clinical pathology include pilocytic astrocytoma, fibrillary astrocytoma, anaplastic astrocytoma, and glioblastoma multiforme. Because astrocytomas are primary brain tumors formed in the brain, they rarely spread to other parts of the body; however, they usually grow rapidly and invade surrounding normal brain tissue and, therefore, are life-threatening.

Risk factors: Brain tumors are caused by mutated or missing genes that result in abnormal cells. High-dose ionizing radiation used over time to treat brain tumors may, on occasion, cause secondary tumors. Over time, exposure to certain chemicals such as pesticides, petrochemicals, formaldehyde, and electromagnetic fields increases the risk of developing astrocytomas. A family history of astrocytomas, as well as increases in age, are also risk factors.

Etiology and the disease process: Generally, malignant brain tumors are caused by changes in genetic structure due to inherited or environmental factors. It was thought that only 5 percent of primary brain tumors, including astrocytomas, are inherited; however, one study has shown that 80 percent of patients with grade IV astrocytoma (glioblastoma multiforme) had anomalous copies of chromosome 7. Familial clustering of gliomas is also associated with defined inherited tumor syndrome, including Li-Fraumeni syndrome, Turcot syndrome, and the neurofibromatosis I syndrome.

Incidence: There were estimated to be about 24,400 new cases of primary malignant brain tumors in the United States in 2023 according to the American Cancer Society. Gliomas of both benign and malignant tumors account for approximately 33 percent of all primary brain tumors; anaplastic astrocytomas accounted for between 3 and 30 percent of gliomas in 2022, while glioblastomas accounted for about 50 percent. Approximately 19,000 people in the United States die of malignant brain tumors every year, which represents between 1 and 2 percent of all cancer-related deaths.

Symptoms: Various symptoms may occur with astrocytomas, which depend largely on the location and size of the tumor. Seizures, focal neurologic deficits such as weakness or speech problems, and headaches are common symptoms. The headaches associated with brain tumors are typically worse in the morning and accompanied by vomiting. Sometimes increased pressure on the brain tissue can cause blurred, double, or even loss of vision. Behavioral changes may also follow with changes in mood and general state of well-being.

Screening and diagnosis: Methods of screening and diagnosing astrocytomas include computed tomography (CT) scans, magnetic resonance imaging (MRI), angiograms, X-rays of the head and skull, and biopsies. Other brain scans, such as magnetic resonance spectroscopy (MRS), single-photon emission computed tomography (SPECT), or positron emission tomography (PET), provide a gauge of brain activity and blood flow. The diagnosis of brain tumors has also been advanced through molecular genetics, which have improved accuracy. Brain tumors are graded based on the following criteria: mitotic index (growth rate), vascularity (blood supply), presence of necrotic center, invasive potential (border distinctness), and similarity to normal cells.

Accordingly, astrocytomas can be graded into four levels. Pilocytic astrocytoma are grade I tumors that are slow-growing and do not invade the surrounding normal tissue, and they are commonly diagnosed in children and young adults. Low-grade astrocytomas, including fibrillary or protoplasmic astrocytomas, are grade II tumors that grow slightly faster than grade I tumors and are invasive, with high incidence in the cerebrums of young adults and in the brain stems of children. Anaplastic astrocytomas are grade III, malignant, and invasive tumors that occur in the same location as low-grade astrocytomas and have a high recurrence rate. Glioblastomas multiforme are grade IV, a malignant type that is by far the most common glioma: Approximately 50 percent of astrocytomas are glioblastomas. The common sites of tumors are cerebral hemispheres in adults and the brain stem in children, and they typically contain more than one cell type.

Treatment and therapy: Treatment options differ according to the size, grade, and location of the tumor. Further, advances in targeted therapies that analyze the genetic composition of the tumor have allowed doctors to tailor treatment to the specific patient and type of brain tumor. Tumors may be removed by craniotomy, an open-skull procedure. They may also be removed by ultrasonic aspiration, in which ultrasonic waves fragment the tumors, which are then aspirated. Alternatively, stereotactic radiosurgery may be performed with a Gamma Knife on benign, malignant, or metastatic tumors that are around 4 centimeters (cm) in size. Chemotherapy may be used as a primary therapy in young children, or as an adjuvant after tumor removal with radiosurgery. For pilocytic and fibrillary astrocytomas, complete resection of the tumor is achieved; however, if excision is not possible because of the tumor’s location, chemotherapy is indicated in young children and radiotherapy in adults. The treatment options for anaplastic astrocytoma and glioblastoma multiforme include total resection followed by radiotherapy and chemotherapy after surgery. Immunotherapies, including those using CAR-T cell technology, can target the specific molecules made by glioblastomas.

Prognosis, prevention, and outcomes: The prognosis and outcome of astrocytomas largely depend on the age of the patient, histological features of the tumor, and degree of neurologic or functional impairment. In low-grade astrocytomas, the mean survival time after surgery is six to eight years, with the prognosis depending on whether the tumor undergoes progression to a malignant phenotype. Complete recovery is possible in pilocytic astrocytoma if total resection is achieved, while fibrillary astrocytomas show frequent recurrence. In patients with anaplastic astrocytomas and glioblastoma multiforme, the extent of resection is a prognostic factor; generally, younger patients below the age of forty-five have a better prognosis.

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