1p/19q codeletion tests detect whether a tumor has lost genetic material from the short arm of chromosome 1 (1p) together with the long arm of chromosome 19 (19q). This combined somatic deletion is a diagnostic marker for oligodendrogliomas and other gliomas, and when present it strongly predicts better response to chemotherapy and radiotherapy and a more favorable prognosis compared with tumors lacking the codeletion. Tests analyze tumor DNA (commonly by FISH, PCR-based assays, array CGH or next‑generation sequencing) to determine whether those chromosomal arms are deleted.

1p/19q codeletion testing is performed on tumor tissue obtained at time of surgical resection or biopsy. Laboratories usually test formalin‑fixed, paraffin‑embedded (FFPE) tissue blocks or unstained slides accompanied by an H&E so a pathologist can identify and mark tumor‑rich areas; fresh‑frozen tissue can be used when available. The pathologist confirms that the selected specimen contains adequate tumor cellularity for reliable DNA analysis.

Some providers also offer testing from circulating tumor DNA (a blood “liquid biopsy”), but this approach is less common and can have lower sensitivity than direct tumor tissue analysis. Follow the laboratory’s submission instructions—typically sending the FFPE block or unstained slides, the H&E, and the completed requisition—to ensure proper handling and accurate results.

If your personal 1p/19q codeletion test shows the codeletion (loss of the short arm of chromosome 1 and the long arm of chromosome 19) in your tumor cells, that result commonly indicates your tumor is an oligodendroglioma subtype that tends to respond better to certain therapies and is associated with a more favorable prognosis compared with tumors that lack the codeletion. A detected codeletion can help your care team choose treatments (for example, specific chemotherapy and radiation approaches) and provide more specific information about likely tumor behavior and expected outcomes.

If the test is negative (no codeletion detected) or the result is unclear or mosaic, it suggests your tumor may be a different glioma subtype and may behave differently; negative results do not necessarily mean a worse outcome in every case, but they do change diagnostic classification and treatment planning. The test reflects genetic changes in the tumor (somatic changes), not inherited cancer risk for you or your relatives, and results should be reviewed with your oncologist or neuro-oncology team who can interpret them alongside pathology, imaging, and other molecular tests to guide care.

1p/19q codeletion testing is a well-established biomarker—when detected as a true whole-arm co-deletion it is highly specific for oligodendroglioma and reliably predicts better response to therapy and prognosis. Common clinical methods (FISH, PCR-based loss-of-heterozygosity assays, array CGH/SNP arrays and NGS-based copy-number analysis) all detect the deletion but differ in their strengths: FISH is widely used and sensitive for routine diagnostics, while array/SNP/NGS approaches are better at distinguishing whole-arm deletions from partial or complex copy-number changes.

Reliability can be reduced by technical and biological factors: low tumor cellularity, DNA quality, partial deletions or polysomy, and intratumoral heterogeneity can cause false negatives or ambiguous results. For these reasons tests should be performed in accredited pathology laboratories and, when results are unexpected or clinically critical, confirmed with an orthogonal method or higher-resolution assay. Interpreting results in the context of histology and other molecular markers gives the most accurate clinical picture.

Test 1p/19q status at diagnosis of a suspected oligodendroglioma or when pathology is unclear—this baseline result is used for prognosis and to guide initial treatment decisions.

Routine, repeat testing is not usually needed because 1p/19q codeletion is generally a stable genomic marker; retesting is appropriate if the tumor recurs or progresses, if a new biopsy is performed, if the original result was inconclusive, or when needed to determine eligibility for a specific therapy or clinical trial—always follow the recommendations of your treating neuro‑oncologist and pathologist.

No, 1p/19q codeletion test results highlight patterns of chromosomal imbalance or resilience in tumor cells rather than providing a standalone medical diagnosis — they are one piece of evidence used to classify tumors and inform prognosis and treatment. These results must be interpreted alongside symptoms, clinical history, imaging, and other laboratory or biomarker data by a qualified clinician.

You cannot change a tumor’s 1p/19q codeletion status — it is a fixed genetic feature of the tumor, not a laboratory value you can “improve.” If a result seems uncertain because of low tumor cellularity or technical issues, ask your treating team about confirmatory testing (different laboratory or methods such as FISH, LOH/array, or NGS) or a repeat biopsy to ensure an accurate result.

What you can do is act on the result: discuss treatment options, prognosis and clinical-trial opportunities with your neuro‑oncologist and a genetic counselor; patients with true 1p/19q codeletion often have different recommended therapies and may respond better to certain chemoradiation approaches. If you have concerns about the original report, request a second opinion or molecular-retesting from a specialized center and follow recommended monitoring and management plans.