{"entity":{"id":"1p19q-codeletion-readout","kind":"biomarker","name":"1p/19q codeletion","aka":["1p/19q codeletion","1p19q codeleted","1p/19q co-deletion","1p19q","whole-arm 1p/19q loss","oligodendroglioma marker"],"tldr":"Loss of one copy each of chromosome arms 1p and 19q, together with an IDH mutation, defines oligodendroglioma in the WHO 2021 classification. It predicts a slower course and a good response to chemotherapy, and separates oligodendroglioma from astrocytoma.","summary":"The whole-arm codeletion is detected by FISH, array or sequencing-based copy-number analysis; partial deletions do not count. WHO CNS5 (2021) requires IDH mutation plus 1p/19q codeletion for the diagnosis of oligodendroglioma, IDH-mutant and 1p/19q-codeleted, grades 2 to 3. The long-term RTOG 9402 and EORTC 26951 results showed that adding PCV chemotherapy to radiotherapy roughly doubled survival in codeleted tumours. Vorasidenib's label covers grade 2 oligodendroglioma by IDH mutation, not by codeletion. As an arm-level change it has no single parent gene and sits under no target here.","asOf":"2026-09-23","links":[{"label":"WHO CNS5 (Louis et al. 2021)","url":"https://doi.org/10.1093/neuonc/noab106"}],"tags":["biomarker","glioma","no-approval"],"related":["idh1-r132","idh2-mutation","mgmt-promoter-methylation"],"cancers":["oligodendroglioma","glioblastoma","idh-mutant-astrocytoma"],"sections":[],"technologies":[],"targets":[],"drugs":["vorasidenib","temozolomide"],"companies":[],"institutions":[],"pathways":[],"terms":["1p19q-codeletion","fish","cytogenetics"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"noParentReason":"Whole-arm loss of chromosome arms 1p and 19q: hundreds of genes, no single parent gene or protein.","measurement":"copy-number","scoringRule":{"text":"Loss of the whole short arm of chromosome 1 and the whole long arm of chromosome 19 by FISH, chromosomal microarray or sequencing copy-number analysis, in a tumour with an IDH1 or IDH2 mutation.","quote":"Oligodendroglioma, IDH-mutant, and 1p/19q-codeleted","source":"https://doi.org/10.1093/neuonc/noab106","sourceLabel":"Louis et al., The 2021 WHO Classification of Tumors of the Central Nervous System, Neuro-Oncology 2021"},"thresholds":[],"definedBy":{"label":"WHO CNS5 classification (Louis et al., Neuro-Oncology 2021)","url":"https://doi.org/10.1093/neuonc/noab106"},"tests":["caris-mi-profile","foundationone-cdx","tempus-xt"],"assays":[],"companionDiagnostics":[],"forPatient":"If your glioma has an IDH mutation and 1p/19q codeletion it is an oligodendroglioma, which grows more slowly and responds well to chemotherapy with radiotherapy. Without the codeletion the same IDH-mutant tumour is an astrocytoma. Vorasidenib is on label for grade 2 tumours of either type after surgery."},"route":"/biomarkers/1p19q-codeletion-readout/","neighbours":{"biomarker":[{"id":"idh1-r132","kind":"biomarker","name":"IDH1 R132 mutation","route":"/biomarkers/idh1-r132/"},{"id":"idh2-mutation","kind":"biomarker","name":"IDH2 mutation (R140 and R172)","route":"/biomarkers/idh2-mutation/"},{"id":"mgmt-promoter-methylation","kind":"biomarker","name":"MGMT promoter methylation","route":"/biomarkers/mgmt-promoter-methylation/"}],"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/"}],"drug":[{"id":"temozolomide","kind":"drug","name":"Temozolomide","route":"/drugs/temozolomide/"},{"id":"vorasidenib","kind":"drug","name":"Vorasidenib","route":"/drugs/vorasidenib/"}],"term":[{"id":"1p19q-codeletion","kind":"term","name":"1p/19q codeletion","route":"/terms/1p19q-codeletion/"},{"id":"cytogenetics","kind":"term","name":"Cytogenetics and karyotype","route":"/terms/cytogenetics/"},{"id":"fish","kind":"term","name":"FISH / ISH (in situ hybridisation)","route":"/terms/fish/"}]}}