OLIGODENDROGLIOMA
1p/19q CO-DELETION & TREATMENT
The only high-grade brain tumour defined by a chromosome deletion — and the most treatment-responsive glioma in neuro-oncology, with median survival exceeding 14 years.
analyticsAt a Glance
- check_circleDefined by IDH mutation PLUS 1p/19q chromosomal co-deletion — both required for diagnosis
- check_circleMedian overall survival 14+ years with PCV chemotherapy and radiotherapy
- check_circleWHO grade 2 and grade 3 subtypes — grade 3 is still one of the most curable high-grade brain tumours
- check_circleCancerFax coordinates expert second opinions and treatment access at leading neuro-oncology centres in China and India
What Is Oligodendroglioma and Why Does 1p/19q Matter?
Oligodendroglioma is a primary brain tumour arising from oligodendrocytes — the glial cells that produce myelin. Since the 2016 WHO CNS tumour classification, its diagnosis is defined not only by histology but by two molecular markers: IDH mutation and 1p/19q chromosomal co-deletion.
“A tumour with IDH mutation alone is not an oligodendroglioma — both the IDH mutation and 1p/19q co-deletion must be present.”
IDH Mutation
IDH1 or IDH2 mutation is the founding event — it creates 2-hydroxyglutarate, which drives epigenetic dysregulation and slower tumour growth compared to IDH-wildtype glioblastoma.
1p/19q Co-Deletion
Loss of the short arm of chromosome 1 (1p) and the long arm of chromosome 19 (19q) is a translocation event unique to oligodendrogliomas — it confirms lineage and is the strongest predictor of chemotherapy sensitivity.
Key Survival and Response Numbers
Oligodendroglioma is the most prognostically favourable high-grade brain tumour. The survival data from landmark trials set it apart from all other gliomas.
- 14.7 yrsMedian OS — Grade 3 with PCV + RT (RTOG 9402)Compared to 7.3 years for radiotherapy alone — the largest survival difference ever seen in a high-grade glioma trial.
- 13.2 yrsMedian OS — Grade 3 with PCV + RT (EORTC 26951)Independent confirmation of the PCV + RT benefit in 1p/19q co-deleted anaplastic oligodendroglioma.
- ~100%IDH mutation rate in oligodendrogliomaBy definition — a tumour without IDH mutation is no longer classified as oligodendroglioma under WHO 2021.
WHO 2021 Classification — Oligodendroglioma Grades
The 2021 WHO CNS5 update simplified oligodendroglioma into two grades. Both require IDH mutation + 1p/19q co-deletion; grade 3 is further defined by CDKN2A/B homozygous deletion or high mitotic activity.
| Parameter | Grade 2 Oligodendroglioma | Grade 3 Oligodendroglioma (Anaplastic) |
|---|---|---|
| IDH mutation | Required | Required |
| 1p/19q co-deletion | Required | Required |
| CDKN2A/B deletion | Absent | Often present — upgrades grade 2 to 3 |
| Mitotic activity | Low | High — Ki-67 typically >5–10% |
| Typical median OS | >15 years with treatment | ~14 years with PCV + RT (landmark trials) |
| Standard treatment | RT ± PCV or temozolomide | RT + PCV (preferred) or RT + temozolomide |
Treatment Approach — From Diagnosis to Long-Term Management
Treatment of oligodendroglioma follows a defined pathway — molecular confirmation first, then surgery, then combined chemoradiation. Long-term follow-up is essential given the slow-growth biology.
- 1
Molecular Pathology Confirmation
IDH status by IHC/sequencing and 1p/19q FISH must be confirmed before finalising treatment. This is not optional — it changes the diagnosis, prognosis, and treatment plan.
- 2
Maximal Safe Surgical Resection
Extent of resection correlates with outcomes. Awake craniotomy is used when the tumour involves eloquent cortex to maximise resection while preserving neurological function.
- 3
Radiotherapy
Standard focal RT to 54–60 Gy in 30–33 fractions targeting the tumour bed with margin. Proton therapy reduces radiation dose to surrounding brain and is increasingly used at specialist centres.
- 4
PCV Chemotherapy (Preferred) or Temozolomide
PCV (procarbazine, lomustine/CCNU, vincristine) given before or after RT demonstrated the 14-year median OS. Temozolomide is used as an alternative — particularly in China and India — given better tolerability.
- 5
Long-Term Surveillance MRI
MRI every 3–6 months for the first 5 years, then annually. Pseudo-progression and treatment-related changes must be distinguished from true progression — this requires specialist neuro-oncology review.
PCV vs Temozolomide: Which Chemotherapy for Oligodendroglioma?
The debate between PCV and temozolomide in 1p/19q co-deleted oligodendroglioma is ongoing. PCV has the longer evidence base from landmark RCTs; temozolomide has a superior tolerability profile and is more widely available.
PCV (Procarbazine / CCNU / Vincristine)
- Landmark RCT data (RTOG 9402, EORTC 26951)The 14.7-year median OS comes specifically from PCV + RT trials — no equivalent 20-year follow-up exists for temozolomide in this disease.
- NCCN and ESMO preferred for grade 3Major guidelines preferentially recommend PCV + RT for anaplastic oligodendroglioma based on Level 1 evidence.
- Potential for deeper molecular responseSome retrospective data suggest PCV achieves higher rates of molecular remission in co-deleted tumours.
Temozolomide
- Superior tolerability profileOral daily dosing with fewer peripheral neuropathy and haematological complications compared to the multi-drug PCV regimen.
- More widely available globallyParticularly relevant for patients in India, Southeast Asia, and the Middle East where CCNU/lomustine procurement is difficult.
- Active CODEL trial evidence pendingThe phase III CODEL trial (RT + PCV vs RT + temozolomide vs temozolomide alone) is expected to provide definitive comparative data.
Landmark Trial Results: PCV + RT in 1p/19q Co-Deleted Oligodendroglioma
Two independent phase III trials confirmed the extraordinary survival benefit of adding PCV chemotherapy to radiotherapy in patients with 1p/19q co-deleted anaplastic oligodendroglioma.
RTOG 9402 — Anaplastic Oligodendroglioma (1p/19q co-deleted)
Source: Cairncross et al, J Clin Oncol 2013; updated follow-up Buckner et al 2016
- Median OS — PCV + RT14.7 yrs
- Median OS — RT alone7.3 yrs
EORTC 26951 — Anaplastic Oligodendroglioma (1p/19q co-deleted)
Source: van den Bent et al, J Clin Oncol 2013
- Median OS — PCV + RT13.2 yrs
- Median OS — RT alone5.7 yrs
Frequently Asked Questions
Common questions from patients and families navigating an oligodendroglioma diagnosis.
How is 1p/19q co-deletion tested?
1p/19q co-deletion is detected by FISH (fluorescence in situ hybridisation) on the tumour tissue. Some centres use next-generation sequencing or chromosomal microarray as alternatives. The test requires adequate tumour tissue from surgery — a core biopsy alone may be insufficient.
If my tumour is IDH-mutant but 1p/19q is not deleted, what does that mean?
IDH-mutant tumours without 1p/19q co-deletion are classified as IDH-mutant astrocytomas under the 2021 WHO classification. These have a different prognosis and treatment approach — they do not carry the same extraordinary chemosensitivity as oligodendroglioma. The distinction is clinically critical.
My pathology report says 'oligodendroglioma-like features' but no molecular testing was done — is that enough?
No. Histological appearance alone is not sufficient for a definitive oligodendroglioma diagnosis under current WHO criteria. Molecular confirmation (IDH mutation + 1p/19q co-deletion) is required. CancerFax can coordinate second-opinion molecular pathology review if your original tissue blocks are available.
Should I have surgery even if the tumour appears in an eloquent area?
Maximal safe resection is recommended in most cases. Awake craniotomy allows continuous neurological monitoring during tumour removal in eloquent areas — skilled neuro-oncological surgeons can often achieve near-total resection with preserved function. The extent of resection is an independent prognostic factor.
Is temozolomide an acceptable alternative to PCV?
Yes, particularly when CCNU (lomustine) is unavailable or when PCV toxicity is a concern. Temozolomide is active in 1p/19q co-deleted tumours, and the ongoing CODEL trial will provide direct comparative data. Most oncologists in India and China use temozolomide + RT as their standard regimen.
Can vorasidenib be used for oligodendroglioma?
Vorasidenib (an IDH1/2 inhibitor) was approved by the FDA in August 2024 for grade 2 IDH-mutant gliomas based on the INDIGO trial. Since all oligodendrogliomas are IDH-mutant, vorasidenib is potentially applicable — particularly for grade 2 oligodendroglioma after surgery, delaying the need for radiotherapy. CancerFax can guide access to vorasidenib via clinical trials or compassionate use.
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