Chromosome 1p: Loss of Heterozygosity (LOH)
**Note 1:** Physician statement of Chromosome 1p deletion/LOH can be used to code this data item.
**Note 2:** This is a special molecular diagnostic test performed on tumor tissue to identify loss of genetic material normally found on the short arm of one of the patient's two copies of chromosome 1. A normal cell will contain two complete copies of each chromosome, one from each parent, and this normal state is termed heterozygous. Loss of heterozygosity (LOH) is an abnormal state reflecting loss of the whole arm of chromosome 1p following a chromosomal translocation event.
**Note 3:** Other terms for LOH include whole arm loss, gene deletion and allelic loss.
**Note 4:** 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.
* 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 5:** 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.
**Note 6:** For brain tumors, tests for LOH of chromosomes 1p and 19q may be performed at the same time and reported on a single report. See also Chromosome 19q: Loss of Heterozygosity (LOH) [NAACCR Data Item #3802]