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1p/19q Deletion in Oligodendrogliomas

3002135

1p19q Deletion by FISH and IDH1 R132H Point Mutation by Immunohistochemistry with Reflex to IDH1 and IDH2 Mutation Analysis, Exon 4 3002135

Method

Fluorescence in situ Hybridization (FISH)/Immunohistochemistry/Polymerase Chain Reaction/Sequencing

Preferred initial test for the diagnosis of oligodendrogliomas
Detect IDH1 or IDH2 mutation and 1p/19q codeletion, which are both necessary for a firm diagnosis of oligodendrogliomas

3001309

1p/19q Deletion by FISH 3001309

Method

Fluorescence in situ Hybridization (FISH)

Use when oligodendrogliomas are suspected

Malignant gliomas (oligodendrogliomas) are the most common type of primary brain tumors. Identification of the 1p/19q deletion is useful in differentiating oligodendrogliomas from astrocytomas and assists in the diagnosis and prognosis of both low- and high-grade oligodendrogliomas, as well as in predicting response to therapy. The 1p/19q deletion should not be used alone for diagnosis.

Disease Overview

Prevalence

Second most common glioma in adults
Accounts for 2% of central nervous system (CNS) tumors

Diagnostic Issues

Malignant gliomas are the most common type of primary brain tumors (>70% of all CNS tumors).

Subtypes are astrocytoma and oligodendroglioma
- Differentiating astrocytoma from oligodendroglioma is crucial
Treatment and prognosis differ between tumors
Combined loss of chromosomal arms 1p and 19q is diagnostic for oligodendrogliomas
Gain of chromosome 19 supports diagnosis of high-grade astrocytoma (glioblastoma)
Loss of 1p may identify treatment-sensitive high-grade oligodendroglioma (for both chemotherapy and radiotherapy)
- Prognostic relevance in low-grade tumors is less well characterized

Genetics

Gene

Chromosomes 1 and 19 involved

Structure/Function

Deletion of short arm of 1p and long arm of 19q results in loss of mediators of resistance to therapy

Variants

1p/19q codeletion is mutually exclusive for TP53 and ATRX mutations and EGFR amplification
1p/19q codeletion is frequently associated with IDH1 or IDH2 variants

Test Interpretation

Results

Positive
- Tumors with 1p/1q ratio <0.80 and ≥24% deleted cells are deemed deleted for 1p
- Tumors with 19q/19p ratio <0.80 and ≥26% deleted cells are deemed deleted for 19q
- Both deletions are associated with a better prognosis
  - Codeletion has better prognosis than single deletion
- Presence of codeletion establishes diagnosis of oligodendroglioma
Negative
- Effectively rules out diagnosis of oligodendroglioma

Limitations

Test should not be used alone for the diagnosis of malignancy

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