What it is
- A combined chromosomal abnormality: deletion of the short arm of chromosome 1 (1p) and the long arm of chromosome 19 (19q).
- Hallmark molecular feature of oligodendrogliomas.
Clinical Relevance
- Diagnostic biomarker:
- The 2021 WHO Classification of CNS Tumors requires IDH mutation + 1p/19q codeletion to diagnose an oligodendroglioma.
- If IDH-mutant but no 1p/19q codeletion → it is classified as astrocytoma instead.
- Prognostic biomarker:
- 1p/19q codeleted tumors have a more favorable prognosis than IDH-mutant astrocytomas or IDH-wildtype gliomas.
- Predictive biomarker:
- Strongly predicts sensitivity to alkylating chemotherapy (e.g., PCV regimen: procarbazine, lomustine [CCNU], vincristine; or temozolomide).
- Patients with codeletion benefit significantly from RT + PCV compared to RT alone.
Pharmacist Pearls
- Always interpret 1p/19q status together with IDH:
- IDH-mutant + 1p/19q codeletion → oligodendroglioma (best prognosis).
- IDH-mutant without 1p/19q codeletion → astrocytoma.
- IDH-wildtype → usually glioblastoma (poorest prognosis).
- Guides long-term treatment planning in neuro-oncology.
- Important for exam prep: 1p/19q codeletion = chemosensitivity + good prognosis.
Summary for oncology pharmacy:
- 1p/19q codeletion is required to define oligodendroglioma (with IDH mutation).
- Predicts better survival and greater benefit from alkylating chemotherapy (PCV or TMZ).