Anaplastic astrocytoma is a malignant brain tumor that grows from star-shaped brain cells called astrocytes. It is classified as a grade 3 tumor on the World Health Organization’s four-tier grading scale, placing it between slower-growing low-grade gliomas and the most aggressive grade 4 tumors like glioblastoma. It is relatively rare, with an incidence of about 0.48 per 100,000 people per year.
How This Tumor Is Classified Today
If you search for anaplastic astrocytoma, you’ll encounter two naming systems. Under the older 2016 WHO classification, this tumor was called “anaplastic astrocytoma, IDH-mutant, WHO grade III.” The 2021 WHO update dropped the word “anaplastic” entirely. The same tumor is now officially called “astrocytoma, IDH-mutant, CNS WHO grade 3.” Many doctors, patients, and medical resources still use the older name, and the tumor itself hasn’t changed. The reclassification reflects a shift toward defining brain tumors by their molecular features, not just how the cells look under a microscope.
The key molecular marker is a mutation in the IDH1 or IDH2 gene. About 60% of anaplastic astrocytomas carry an IDH1 mutation, and this single feature matters more for predicting outcomes than almost anything else about the tumor. Patients with IDH-mutant anaplastic astrocytomas live significantly longer than those whose tumors lack the mutation. In fact, patients with IDH-wild-type (non-mutated) anaplastic astrocytomas tend to fare worse than patients with IDH-mutant glioblastomas, even though glioblastoma is technically a higher-grade tumor. This finding is one of the reasons the WHO shifted to a molecular-first classification system.
Common Symptoms
Seizures are often the first sign, particularly in slower-growing tumors. A first-time seizure in an adult with no prior history is one of the most common reasons these tumors get discovered. Other early symptoms include subtle changes in thinking, mood, or memory, difficulty finding the right words, vision changes, clumsiness or weakness on one side of the body, and tingling or numbness that spreads into an arm or leg.
As the tumor grows, symptoms tend to worsen and expand. Speech and vision problems become more pronounced, balance deteriorates, and cognitive decline becomes more noticeable to the person and those around them. Headaches, particularly ones that are worse in the morning, can develop or intensify. Because many of these symptoms overlap with other conditions, imaging is essential for diagnosis.
How It’s Diagnosed
MRI is the primary imaging tool. On scans, anaplastic astrocytomas typically appear as irregular masses that show up bright on T2-weighted images and dark on T1-weighted images. They often show some degree of contrast enhancement when a gadolinium-based dye is injected, along with surrounding swelling. Distinguishing an anaplastic astrocytoma from a glioblastoma on imaging alone can be difficult because both tumors look similar, with differences in enhancement and tissue death patterns that are often too subtle for the human eye to reliably detect.
A definitive diagnosis requires tissue, usually obtained through a biopsy or during surgical removal. Pathologists examine the cells and run molecular tests, looking specifically for IDH mutations and other genetic markers that determine the exact tumor type and grade under current WHO criteria.
Why Surgery Matters
Removing as much of the tumor as safely possible is the first step in treatment, and the extent of that removal has a dramatic effect on outcomes. In one study of anaplastic gliomas, patients who had a complete (gross total) resection had a 10-year overall survival rate of about 70%. Those who had a subtotal resection, where most but not all of the tumor was removed, had a 10-year survival rate around 53%. For patients who could only have a partial resection or biopsy, that number dropped to roughly 21%.
Recurrence rates tell a similar story. Only about 34% of patients with complete or subtotal resections saw their tumors return, compared to 83% of those who had only a partial resection or biopsy. The challenge is that these tumors grow within functioning brain tissue, so “maximal safe resection” means taking out as much tumor as possible without causing new neurological damage. The location of the tumor within the brain is a major factor in how much can be safely removed.
Radiation and Chemotherapy
After surgery, most patients receive radiation therapy followed by or combined with chemotherapy. Standard radiation delivers focused beams to the tumor area over several weeks. Chemotherapy is typically given in cycles, with treatment days followed by rest periods to allow the body to recover. A common schedule involves treatment for five days out of every 28-day cycle, repeated for several months.
The tumor’s molecular profile helps guide treatment decisions. Tumors with IDH mutations and a feature called MGMT promoter methylation (which affects how well cells can repair damage from chemotherapy) tend to respond better to treatment. These markers, along with the extent of surgical resection, are the strongest predictors of how well treatment will work.
Survival and Prognosis
The five-year relative survival rate for diffuse and anaplastic astrocytomas combined is about 49%, according to the most recent SEER data covering 2015 through 2022. That number blends together patients with very different molecular profiles, and the range of individual outcomes is wide.
IDH mutation status creates the sharpest dividing line. Patients whose tumors carry an IDH1 mutation have substantially better outcomes than those without it. Age at diagnosis also plays a significant role, though much of that effect traces back to the fact that IDH mutations are far more common in younger patients. Younger adults with IDH-mutant tumors represent the most favorable end of the spectrum, while older patients with IDH-wild-type tumors face the most challenging prognosis.
Anaplastic astrocytomas can recur after treatment, sometimes as the same grade and sometimes as a higher-grade tumor. Follow-up imaging at regular intervals is standard practice to monitor for regrowth, and treatment options at recurrence may include additional surgery, re-irradiation, or different chemotherapy approaches depending on the individual situation.
IDH-Targeted Treatments
Because IDH mutations are so central to this tumor’s biology, drugs that specifically block mutant IDH proteins are an active area of interest. Vorasidenib, a drug designed to cross the blood-brain barrier and inhibit both mutant IDH1 and IDH2, showed promising results in a clinical trial published in the New England Journal of Medicine for patients with grade 2 gliomas who had not yet received other cancer therapy. Whether vorasidenib will prove equally effective for grade 3 tumors, either alone or combined with other treatments, is still being evaluated in additional trials.