Chromosome 1p: Loss of Heterozygosity (LOH)
Description
Chromosome 1p: Loss of Heterozygosity (LOH) refers to the loss of genetic material normally found on the short arm of one of the patient's two copies of chromosome 1. Codeletion of Chromosome 1p and 19q is a diagnostic, prognostic and predictive marker for gliomas and is strongly associated with the oligodendroglioma phenotype.
Loss of Heterozygosity Chromosome 1 p and Chromosome 19q are two genetic tests that are frequently done at the same time and reported together. Loss of heterozygosity (LOH) in a chromosome means that genetic material normally found in a specific area of a chromosome is missing. In other words, this is damage to the chromosome that results in failure of tumor suppression, which in turn may cause the development or progression of a malignancy. For 1p LOH, the specific chromosomal defect is on the short arm (p) of chromosome 1. For 19q LOH, the specific chromosomal defect is on the long arm (q) of chromosome 19.
Normal cells have two complete copies of each chromosome, a state called heterozygosity. The loss of this section of the chromosome is associated with improved outcome. It can be used to aid diagnosis and to make treatment decisions because sensitivity to chemotherapy agents, such as lomustine, procarbazine, and vincristine, is increased with either 1p or 19q LOH. Special molecular diagnostic (polymerase chain reaction or gene amplification) tests look for missing genetic material. LOH for chromosome 1p and 19q is tested primarily for oligodendroglioma, anaplastic oligodendroglioma, oligoastrocytoma, and anaplastic oligoastrocytoma. It is infrequently tested for other gliomas, such as glioblastoma multiforme.
Rationale
Chromosome 1p: Loss of Heterozygosity (LOH) is a Registry Data Collection Variable in AJCC. It was previously collected as Brain, CS SSF #5.
Additional Info
**Source documents:** pathology report
**Other names include** whole arm loss, allelic loss, gene deletion, 1p/19q fragment analysis
Notes
**Note 1:** **Physician Statement**
* Physician statement of Chromosome 1p deletion/LOH can be used to code this data item when no other information is available.
**Note 2:** **Applicable histologies**
* Below is a list of histologies/terms for which the Chromosome 1p test is commonly done. If the test was done, record the results, regardless of the histology. If the histology is not listed among those for which the Chromosome 1p test is commonly done, and the test result is not readily available, assume it was not done and code 9 for unknown.
* 9382/3: Oligoastrocytoma (anaplastic, or NOS)
* 9400/3: Diffuse astrocytoma (IDH mutant, IDH wild type, or NOS)
* 9401/3: Anaplastic astrocytoma (IDH mutant, IDH wild type, or NOS)
* 9411/3: Gemistocytic astrocytoma, IDH mutant
* 9424/3: Anaplastic pleomorphic xanthoastrocytoma
* 9430/3: Astroblastoma
* 9440/3: Glioblastoma (epithelioid, IDH wild type, or NOS)
* 9441/3: Giant cell glioblastoma
* 9442/3: Gliosarcoma
* 9445/3: Glioblastoma, IDH mutant
* 9450/3: Oligodendroglioma (IDH mutant and 1p/19q codeleted, or NOS)
* 9451/3: Anaplastic oligodendroglioma (IDH mutant and 1p/19q codeleted, or NOS)
* 9505/3: Anaplastic ganglioglioma
* 9530/3: Anaplastic (malignant) meningioma
**Note 3:** **Related data item**
* See also 3802: Chromosome 19q: Loss of Heterozygosity (LOH).
Coding Guidelines
**1)** **Code 0** when the 1p/19q is not identified/not present
**2)** **Code 1** when the 1p/19q is present
**3)** **Code 6** for **Benign (/0)** or **Borderline (/1) tumors**
**4)** **Code 9** when
* **a.** No documentation in the medical record
* **b.** 1p/19q test not done (not assessed)
* **c.** Unknown if 1p/19q test was performed (unknown if assessed)
Default
8
Metadata
SSDI
| Code |
Description |
| 0 |
Chromosome 1p deletion/LOH not identified/not present |
| 1 |
Chromosome 1p deletion/LOH identified/present |
| 6 |
Benign or borderline tumor |
| 7 |
Test ordered, results not in chart |
| 8 |
Not applicable: Information not collected for this case
(If this item is required by your standard setter, use of code 8 will result in an edit error.) |
| 9 |
Not documented in medical record
Cannot be determined by the pathologist
Chromosome 1p deletion/LOH not assessed or unknown if assessed |
