Loss of heterozygosity

Originally, a heterozygous state is required and indicates the absence of a functional tumor suppressor gene copy in the region of interest.

[2] Other commonly lost chromosomal loci are still being investigated in terms of potential tumor suppressors located in those regions.

This acquired homozygosity could lead to development of cancer if the individual inherited a non-functional allele of a tumor suppressor gene.

The classical example of such a loss of protecting genes is hereditary retinoblastoma, in which one parent's contribution of the tumor suppressor Rb1 is flawed.

[citation needed] In breast, ovarian, pancreatic, and prostate cancers, a core enzyme employed in homologous recombination repair (HRR) of DNA damage is often defective due to LOH, that is genetic defects in both copies (in the diploid human genome) of the gene encoding an enzyme necessary for HRR.

Genome-wide LOH status of fresh or paraffin embedded tissue samples can be assessed by virtual karyotyping using SNP arrays.