====== Oligodendroglioma, IDH-mutant and 1p/19q-codeleted ======

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**Source**: WHO Classification of Tumors of the Central Nervous System, 5th Edition (2021)

**Definition**:  
Oligodendroglioma, IDH-mutant and 1p/19q-codeleted, is a **diffuse glioma** defined molecularly by the presence of an **IDH1 or IDH2 mutation** and a **combined whole-arm codeletion of chromosomal arms 1p and 19q**. Both alterations are required for diagnosis.

===== Key Features =====
  * **Type**: Diffuse glioma of oligodendroglial lineage
  * **Molecular markers**: 
    * IDH1 or IDH2 mutation
    * Whole-arm 1p/19q codeletion
  * **WHO Grades**: 2 or 3
  * **Typical location**: Cerebral hemispheres, most commonly the frontal lobes
  * **Histopathology**:
    * Round, uniform nuclei with perinuclear clearing ("fried egg" appearance)
    * Delicate, branching capillary network ("chicken wire" vasculature)
    * Calcifications common
  * **Imaging**: Often well-demarcated lesion with calcifications on CT or MRI
  * **Prognosis**: Favorable compared to IDH-mutant astrocytomas; sensitive to chemotherapy and radiotherapy

===== Diagnostic Criteria =====
  - Diffuse glioma histology
  - Confirmed **IDH1/IDH2 mutation** (by sequencing or immunohistochemistry)
  - **Codeletion of 1p and 19q** (typically via FISH, PCR-based LOH analysis, or DNA methylation profiling)
  - No ATRX loss (ATRX retained)
  - No TP53 overexpression

===== Treatment Options =====

see [[Oligodendroglioma treatment]]


===== Notes =====
  * Without 1p/19q codeletion, the tumor should be classified as an **astrocytoma** (if IDH-mutant) or **glioblastoma** (if IDH-wildtype).
  * 1p/19q codeletion is associated with better prognosis and increased treatment responsiveness.