# 1p/19q codeletion

Source: https://onco.cc/terms/1p19q-codeletion/  
OnCo record `1p19q-codeletion` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Loss of one whole arm each of chromosomes 1 and 19, together with an IDH mutation, is what now defines an oligodendroglioma; a codeleted tumour grows slowly and responds to PCV chemotherapy plus radiotherapy for many years, so the test decides both the diagnosis and the treatment plan.

## Summary

What is measured: whole-arm loss of 1p and 19q, the product of an unbalanced translocation t(1;19)(q10;p10). How: FISH with 1p36 and 19q13 probes (partial deletions can mimic it and are not the same lesion), copy-number from methylation or SNP arrays, or next-generation sequencing panels that call copy number; WHO 2021 requires an IDH mutation plus 1p/19q codeletion for oligodendroglioma, grade 2 or 3, while an IDH-mutant astrocytoma is 1p/19q intact and usually shows ATRX loss and TP53 mutation, with CDKN2A/B homozygous deletion making it grade 4. TERT promoter mutation is almost universal in oligodendroglioma, with CIC and FUBP1 mutations. What a positive result changes: radiotherapy followed by PCV (procarbazine, lomustine, vincristine) roughly doubled median survival in the RTOG 9402 and EORTC 26951 trials (about 14 years against 7 with radiotherapy alone) and remains the standard for grade 3 and high-risk grade 2 disease; vorasidenib is an option for residual or recurrent grade 2 IDH-mutant glioma whether codeleted or not (INDIGO); younger patients with a gross total resection can be watched; a non-codeleted result sends the patient down the astrocytoma path of radiotherapy with temozolomide (CATNON). Where it matters: oligodendroglioma, IDH-mutant astrocytoma and glioblastoma work-up.

## Fields

- Kind: Term
- Last checked: 2026-09-17
- Also known as: 1p/19q; 1p19q; 1p/19q co-deletion; 1p/19q-codeleted; codeletion; codeleted; 1p/19q intact; non-codeleted; whole-arm 1p/19q loss; t(1;19)(q10;p10)

## Connected records

- targets: [IDH1 / IDH2](https://onco.cc/targets/idh/)
- terms: [CDKN2A/B homozygous deletion](https://onco.cc/terms/cdkn2a-homozygous-deletion/), [Extent of resection (RANO resect classes)](https://onco.cc/terms/extent-of-resection/), [FISH / ISH (in situ hybridisation)](https://onco.cc/terms/fish/), [MGMT promoter methylation](https://onco.cc/terms/mgmt/), [TERT promoter mutation](https://onco.cc/terms/tert-promoter/)
- technologies: [Methylation classifier for brain tumours](https://onco.cc/technologies/cns-tumour-methylation-classifier/)
- drugs: [Temozolomide](https://onco.cc/drugs/temozolomide/), [Vorasidenib](https://onco.cc/drugs/vorasidenib/)
- cancers: [Astrocytoma, IDH-mutant (grades 2 to 4)](https://onco.cc/cancers/idh-mutant-astrocytoma/), [Glioma & glioblastoma](https://onco.cc/cancers/glioblastoma/), [Oligodendroglioma, IDH-mutant and 1p/19q-codeleted](https://onco.cc/cancers/oligodendroglioma/)

---
JSON: https://onco.cc/api/v1/entities/1p19q-codeletion.json