No, Grade 3 Oligodendroglioma is NOT Low-Grade
Grade 3 oligodendroglioma (formerly called anaplastic oligodendroglioma) is classified as a high-grade tumor, not a low-grade tumor. 1, 2
Grading Classification
The WHO classification system divides oligodendrogliomas into two distinct grades:
- Grade 2 oligodendroglioma = Low-grade tumor
- Grade 3 oligodendroglioma = High-grade tumor (anaplastic)
Key Distinguishing Features
Grade 3 oligodendrogliomas are distinguished from Grade 2 by:
- High mitotic activity (numerous cell divisions)
- Microvascular proliferation (abnormal blood vessel growth)
- Frequently present necrosis (dead tissue areas)
- Increased cellularity
In contrast, Grade 2 oligodendrogliomas show no or very few mitoses and lack these aggressive features. 2
Clinical Implications of the Grade 3 Designation
The high-grade classification directly impacts treatment intensity. For Grade 3 oligodendroglioma (IDH-mutant, 1p/19q-codeleted), the standard of care is radiation therapy followed by PCV chemotherapy (procarbazine, lomustine, vincristine), with temozolomide as a reasonable alternative when toxicity is a concern. 1, 2
This aggressive treatment approach reflects the higher-grade nature of these tumors. Large randomized controlled trials demonstrated that adding PCV to radiotherapy approximately doubled overall survival in these patients. 1
Important caveat: While Grade 3 is technically higher grade, the distinction between Grade 2 and Grade 3 in 1p/19q-codeleted oligodendrogliomas remains somewhat controversial. 1 Some younger patients (<40 years) with complete resection and favorable molecular features (no homozygous CDKN2A/B deletion) may be considered for watch-and-wait strategies even with Grade 3 tumors, though this is not standard practice. 1
The terminology can be confusing because "low-grade glioma" is sometimes used colloquially to refer to Grade 2 tumors specifically, while Grade 3 tumors are considered high-grade or anaplastic tumors. 3, 4