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If your pathology report mentions 1p/19q codeletion, it points to an oligodendroglioma — usually a slower-growing, more treatable glioma. Here is what the marker means, how it is tested, and why it shapes your plan.
Reading a brain-tumour pathology report can feel like reading a foreign language. If yours mentions 1p/19q codeletion, here is the simple version: your tumour cells have lost one whole copy of the short arm of chromosome 1 (the 1p arm) and one whole copy of the long arm of chromosome 19 (the 19q arm) — together, as a pair. That paired, whole-arm loss is the genetic fingerprint of an oligodendroglioma.
On balance, this is reassuring news. Among the diffuse gliomas that affect adults, tumours carrying the 1p/19q codeletion tend to grow more slowly and respond better to radiation and chemotherapy than gliomas without it. It does not mean the tumour is harmless — oligodendrogliomas are still malignant — but it usually places you in the more treatable group, and it directly shapes the treatment your team will recommend. This page is part of CION's wider guide to the brain cancer & brain tumour hub.
Under the WHO 2021 Classification of Tumours of the Central Nervous System, the diagnosis of oligodendroglioma now requires both an IDH mutation and 1p/19q codeletion — the appearance of the cells under the microscope is no longer enough on its own. NCCN and EANO glioma guidelines build their treatment recommendations around exactly these molecular markers.
A single molecular result is never enough. IDH status and the 1p/19q result are read together to decide which type of diffuse glioma you have. This is the heart of the modern, molecular approach to brain-tumour diagnosis.
When a diffuse glioma is both IDH-mutant and 1p/19q-codeleted, it is classified as an oligodendroglioma (WHO Grade 2 or 3). This is the most favourable molecular group among adult diffuse gliomas — slower-growing, and historically the group that gains the most from adding chemotherapy to radiation.
An IDH-mutant glioma without the 1p/19q codeletion is an astrocytoma, not an oligodendroglioma. It behaves and is treated differently. A third group — IDH-wildtype glioma — is more aggressive again. This is why the panel, not a single test, decides the diagnosis. Learn more about molecular testing of brain tumours.
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Newly diagnosed, or unsure whether IDH and 1p/19q testing has been done? CION's neuro-oncology team will review your reports and explain your options clearly.
The 1p/19q test is done on tumour tissue — taken at surgery or from a biopsy — not on a blood sample. The laboratory looks directly at the chromosomes inside the tumour cells to confirm whether both the 1p and 19q arms have been lost together.
The 1p/19q result is not just a label on a report — it changes what your team recommends. For a confirmed, codeleted oligodendroglioma, treatment is built around the modalities CION delivers directly, with surgery coordinated through neurosurgical partners.
A full walk-through of surgery, radiation, chemotherapy and tumour-board care sits on our brain tumour treatment in Hyderabad page. To talk through your own report, book a free consultation or call 18002028726.
Oligodendrogliomas are graded WHO Grade 2 (slower-growing) or Grade 3 (more active) — never Grade 4. Among adult diffuse gliomas, the 1p/19q-codeleted group has the most favourable outlook, and many people live for many years with treatment and careful monitoring.
We deliberately avoid quoting a single survival number on this page. Published outcomes from sources such as NCCN, EANO and SEER are reported as ranges that vary widely by grade, age, how much tumour was removed, and how the tumour responds to treatment. A meaningful figure for you can only come from your own grade and situation, discussed honestly with your oncologist — never as a guarantee.
What is consistent across the evidence is that this molecular group responds well to combined radiation and alkylating chemotherapy, and that slow growth allows time to plan care thoughtfully rather than rush. For a deeper look at the tumour type itself, see our oligodendroglioma overview.
The survival benefit of adding chemotherapy to radiation for 1p/19q-codeleted oligodendroglioma was established by long-term randomised trials — RTOG 9402 and EORTC 26951 — both of which showed that the codeleted group, specifically, lived significantly longer when PCV chemotherapy was added. This is why your 1p/19q result, not just the appearance of the tumour, guides the chemotherapy decision in NCCN and EANO guidelines.
For a glioma diagnosis, a second opinion is especially valuable in a few specific situations:
CION offers a dedicated, free written second-opinion service through its neuro-oncology tumour board. Request your free second opinion or call 18002028726 — bring your MRI, pathology report and any molecular results, and we will review them with you.
If IDH and 1p/19q testing has not been confirmed on your biopsy, a free written second opinion from CION's tumour board can make sure your diagnosis — and your plan — rest on complete information.
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Start Your Story. Book Free Consultation.It means your tumour has lost one copy of the short arm of chromosome 1 (the "1p" arm) and one copy of the long arm of chromosome 19 (the "19q" arm) together. This combined whole-arm loss is the genetic signature of an oligodendroglioma. Under the WHO 2021 classification, a diffuse glioma is only called an oligodendroglioma if it is both IDH-mutant and 1p/19q-codeleted. The codeletion is good news on balance — these tumours are usually slower-growing and tend to respond well to chemotherapy and radiation, with longer survival than other adult gliomas at the same grade.
Oligodendrogliomas are malignant (cancerous) brain tumours, but they sit at the slower-growing, more treatable end of the glioma spectrum. They are graded Grade 2 or Grade 3 under the WHO system — never Grade 4. Many people live a long time with the right treatment, and a number have stable disease for many years. The 1p/19q codeletion is one reason for this favourable behaviour. Your exact outlook depends on grade, age, how much tumour was removed, and your symptoms — questions a neuro-oncology team can talk through with you using your own scans and reports.
Because it changes the plan in concrete ways. NCCN and EANO guidelines recommend that 1p/19q-codeleted oligodendrogliomas be considered for radiation followed by PCV chemotherapy (an alkylating-chemotherapy combination), as this group historically gains the most survival benefit from adding chemotherapy to radiation. Tumours without the codeletion are managed differently. So the test result is not just a label — it directly guides whether and which chemotherapy is offered, and helps your team set realistic expectations. This is why molecular testing should be done on every diffuse glioma biopsy.
It is done on the tumour tissue obtained at surgery or biopsy — not on a blood sample. The lab examines the chromosomes in the tumour cells using techniques such as FISH (fluorescence in situ hybridisation), or molecular methods like next-generation sequencing that detect the same whole-arm loss. IDH mutation status is tested on the same sample. At CION, we arrange IDH and 1p/19q testing as standard on diffuse-glioma biopsies, and have outside slides re-read so the diagnosis is built on complete molecular information before any treatment decision is made.
Yes — and this distinction is central to the WHO 2021 system. An IDH-mutant glioma without 1p/19q codeletion is classified as an astrocytoma, not an oligodendroglioma. An IDH-mutant glioma with 1p/19q codeletion is an oligodendroglioma. Both are different again from IDH-wildtype glioblastoma. The two markers are read together: IDH mutation places the tumour in the more favourable family, and the 1p/19q result then separates oligodendroglioma from astrocytoma. This is why a single marker is never enough — the full panel decides the diagnosis and the treatment path.
Among adult diffuse gliomas, 1p/19q-codeleted oligodendrogliomas have the most favourable outlook, and published studies report median survival measured in many years — longer for Grade 2 than Grade 3, and longer in younger patients with more complete surgery. We deliberately avoid quoting a single number here: outcomes vary widely by grade, age, extent of removal, and response to treatment, and ranges from sources like NCCN and EANO are best discussed against your own situation. What is consistent across studies is that this molecular group responds well to combined radiation and chemotherapy. Bring your reports to a free consultation for an honest, personalised discussion.
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