{"entity":{"id":"1p19q-codeletion","kind":"term","name":"1p/19q codeletion","aka":["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)"],"tldr":"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.","asOf":"2026-09-17","links":[],"tags":[],"related":["idh","fish","cns-tumour-methylation-classifier","cdkn2a-homozygous-deletion","tert-promoter","mgmt","temozolomide","vorasidenib","extent-of-resection"],"cancers":["oligodendroglioma","idh-mutant-astrocytoma","glioblastoma"],"sections":[],"technologies":[],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"category":"Biomarkers"},"route":"/terms/1p19q-codeletion/","neighbours":{"target":[{"id":"idh","kind":"target","name":"IDH1 / IDH2","route":"/targets/idh/"}],"term":[{"id":"cdkn2a-homozygous-deletion","kind":"term","name":"CDKN2A/B homozygous deletion","route":"/terms/cdkn2a-homozygous-deletion/"},{"id":"extent-of-resection","kind":"term","name":"Extent of resection (RANO resect classes)","route":"/terms/extent-of-resection/"},{"id":"fish","kind":"term","name":"FISH / ISH (in situ hybridisation)","route":"/terms/fish/"},{"id":"mgmt","kind":"term","name":"MGMT promoter methylation","route":"/terms/mgmt/"},{"id":"tert-promoter","kind":"term","name":"TERT promoter mutation","route":"/terms/tert-promoter/"}],"technology":[{"id":"cns-tumour-methylation-classifier","kind":"technology","name":"Methylation classifier for brain tumours","route":"/technologies/cns-tumour-methylation-classifier/"}],"drug":[{"id":"temozolomide","kind":"drug","name":"Temozolomide","route":"/drugs/temozolomide/"},{"id":"vorasidenib","kind":"drug","name":"Vorasidenib","route":"/drugs/vorasidenib/"}],"cancer":[{"id":"idh-mutant-astrocytoma","kind":"cancer","name":"Astrocytoma, IDH-mutant (grades 2 to 4)","route":"/cancers/idh-mutant-astrocytoma/"},{"id":"glioblastoma","kind":"cancer","name":"Glioma & glioblastoma","route":"/cancers/glioblastoma/"},{"id":"oligodendroglioma","kind":"cancer","name":"Oligodendroglioma, IDH-mutant and 1p/19q-codeleted","route":"/cancers/oligodendroglioma/"}]}}