Oligodendrogliomas arise from cells resembling oligodendrocytes — the glial cells that make myelin, the insulation around nerve fibers. Among the diffuse gliomas, they are the type most often associated with a more favorable course.
What makes an oligodendroglioma an oligodendroglioma, under current rules, is a precise molecular definition: the tumor must be IDH-mutant and have 1p/19q codeletion. That second term means the tumor has lost specific pieces of two chromosomes (the short arm of chromosome 1 and the long arm of chromosome 19). This combination is the genetic signature that defines the type — appearance alone is no longer enough to make the diagnosis.
Why does this matter so much? Because the 1p/19q-codeleted, IDH-mutant signature is associated with better response to treatment and longer survival compared with many other diffuse gliomas. Historically, these tumors were noted to respond particularly well to a chemotherapy combination, and that observation helped shape today's understanding of the tumor's biology.
Oligodendrogliomas are graded 2 or 3. Grade 3 grows more actively than grade 2, but even grade 3 oligodendrogliomas often carry a more favorable outlook than other grade 3 gliomas. Seizures are a common first symptom, and many patients are diagnosed after a seizure leads to an MRI.
Treatment is individualized, but commonly involves surgery to remove as much as is safely possible and to confirm the molecular diagnosis, often followed by radiation and chemotherapy depending on grade and other factors. For certain IDH-mutant grade 2 oligodendrogliomas after surgery, the targeted drug vorasidenib is now an option. As always, "more favorable" does not mean harmless — oligodendrogliomas still require expert treatment and long-term monitoring.