Diffuse astrocytoma (grade II)
Diffuse astrocytoma is a slow-growing brain tumor that is thought to arise from astrocytes, the supportive cells in the nervous system.
Normally, astrocytes are responsible for a variety of roles, including providing nutrients to neurons, maintaining the blood-brain barrier, and modulating neurotransmission (how neurons communicate with each other).
Diffuse astrocytoma, as the name suggests, is a tumor with ill-defined boundaries – small clusters of tumor cells tend to grow into and infiltrate neighboring, healthy tissue. For this reason, it may be difficult to completely remove these tumors during surgery. These types of tumors tend to arise in the cerebral hemispheres of the brain.
Diffuse astrocytomas are a specific type of astrocytoma, and also belong to the broader category of diffuse gliomas – diffuse tumors that arise from glial cells. This is because astrocytes are a type of glial cell. For this reason, diffuse astrocytoma (grade II) may also be called a “low-grade glioma.”
Some common symptoms may include the following:
Additional symptoms depend on the size and location of the tumor, which may impact specific neurological functions. For example, a diffuse astrocytoma near the motor cortex (which controls body movement) may cause slowly progressive weakness on one side of the body.
Diffuse astrocytoma is the second most common glioma, after glioblastoma, accounting for about 2-5% of all primary brain tumors in adults.1 In 2017, an estimated 1,410 new cases were diagnosed in the United States.1 Most cases of diffuse astrocytoma occur in adults, although they occasionally develop in children as well.
Diffuse astrocytoma can be further classified into more specific subtypes based on genetic characteristics. Specifically, diffuse astrocytomas can have abnormal genetic signatures, including mutations in the IDH1 or IDH2 genes. The presence of these genetic differences can affect prognosis and treatment, and are classified accordingly:
- Diffuse astrocytoma, IDH-mutant (if a mutation in either IDH1 or IDH2 is detected)
- Diffuse astrocytoma, IDH-wildtype (if no IDH mutations are detected)
- Diffuse astrocytoma, Not otherwise specified (if the tumor has not been tested)
Depending on the size and location of the tumor, patients with diffuse astrocytoma are usually first treated with surgery. The primary objective is to remove as much of the tumor as possible, while protecting critical brain function–this is called “maximal safe resection”. Especially since diffuse astrocytomas can occur in near areas of the brain that control body movement, language, or vision, special measures may be taken to protect these functions. For example, awake surgery with brain mapping is commonly used when tumors are located in the brain regions that control language or movement. This technique allows surgeons to safely identify and preserve critical brain regions.
Chemotherapy and radiation may also be suggested in addition to surgery, depending on the tumor’s size, location, and extent of surgical removal, among others. Depending on whether the tumor is classified as IDH-mutant or -wildtype, certain therapies may be considered.
How well a patient with diffuse astrocytoma responds to treatment depends on a variety of factors, including the tumor’s genetic classification (e.g. IDH-mutant, IDH-wildtype). In general, IDH-mutant diffuse astrocytomas respond better to treatment and have improved prognoses.2
Typically, complete surgical removal of the tumor offers the best patient outcomes for long-term survival. However, diffuse astrocytoma can recur after surgery, so patients are regularly monitored for both tumor recurrence and progression to a higher grade tumor.
Grade II diffuse gliomas, often referred as low-grade gliomas, are slow-growing tumors and hold a better prognosis than grade III-IV diffuse gliomas, which are high-grade gliomas, and progress more rapidly.
Finding information about prognoses and survival rates is a personal decision. The current statistics are only summary data, and don’t necessarily reflect results from new or experimental therapies. These data do not determine how individual patients might respond to their treatment – everyone is different. That said, some people may choose to look for this information, which can be found in the most recent CBTRUS Statistical Report, in Tables 21-25.1
- Ostrom, Q.T., et al., CBTRUS Statistical Report: Primary brain and other central nervous system tumors diagnosed in the United States in 2010-2014. Neuro Oncol, 2017. 19(suppl_5): p. v1-v88.
- Siegal, T., ed. Clinical Relevance of Prognostic and Predictive Molecular Markers in Gliomas. Advances and Technical Standards in Neurosurgery, ed. J. Schramm. Vol. 43. 2016, Springer. 91-108.
This content was reviewed by UCSF Neuro-Oncology Fellow, Sarah Lapointe MD.