Understanding the HRD result

The HRD test result will either show a positive or negative HRD status. A positive status is defined as either the presence of a BRCA mutation or a high genomic instability score. The genomic instability score is the combination of other genomic instabilities (besides BRCA status) and may include loss of heterozygosity (LOH), telomeric allelic imbalance (TAI) and large-scale state transitions (LST).1,2

The HRD test result will either show a positive or negative HRD status. A positive status is defined as either thepresence of a BRCA mutation or a high genomic instabilityscore. The genomic instability score is the combination ofother genomic instabilities (besides BRCA status) and mayinclude loss of heterozygosity (LOH), telomeric allelicimbalance (TAI) and large-scale state transitions (LST).1,2

The genomic instability score will be defined according to the type of test. The score is a range and contains a threshold, where scores above the threshold are determined as HRD-positive. Genomic instability scores are frequently included in the test results/report.

HRD-positive1,2

Positive for genomic instability

Based on a high genomic instability score from either LOH or a combination of LOH, TAI and LST

or

Positive for BRCA1/2 mutation

Based on the presence of a deleterious or suspected deleterious sequencing mutation or large rearrangement of BRCA1/2

HRD-negative1,2

Negative for genomic instability

Based on a low genomic instability score from either LOH or a combination of LOH, TAI and LST

and

Negative for BRCA1/2 mutation

Based on the absence of a deleterious or suspected deleterious sequencing mutation or large rearrangement of BRCA1/2

Click here for more information on deleterious and suspected deleterious mutations

1. Myriad Genetic Laboratories, Inc. myChoice® CDx Technical Information. Available at: https://myriad-web.s3.amazonaws.com/myChoiceCDx/downloads/myChoiceCDxTech.pdf (Accessed July, 2021); 2. Foundation Medicine, Inc. FoundationFocus™ CDxBRCA LOH Technical Information Summary. Available at: https://www.accessdata.fda.gov/cdrh_docs/pdf16/P160018S001c.pdf (Accessed July, 2021)

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