# HRD & BRCA testing

Source: https://onco.cc/technologies/hrd-testing/  
OnCo record `hrd-testing` (Technology). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Tests that reveal whether a tumour has a broken DNA repair system, which predicts response to PARP inhibitors and platinum.

## Summary

HRD and BRCA testing identifies tumours whose homologous recombination DNA repair is defective and therefore vulnerable to PARP inhibitors and platinum. It combines germline and somatic BRCA1/2 sequencing with genomic-scar scores such as the myChoice CDx genomic instability score and FoundationOne LOH, which sum loss of heterozygosity, telomeric allelic imbalance and large-scale transitions into one measure. This extends PARP-inhibitor benefit beyond BRCA carriers. The scar, however, is permanent: it persists even after reversion mutations restore repair and resistance emerges, and the thresholds defining HRD-positive are still debated. Functional assays such as RAD51 foci and mutational signature 3 are emerging alternatives that may capture current repair status. These tests reveal whether a tumour's DNA repair is broken, which predicts response to PARP inhibitors and platinum.

## Fields

- Kind: Technology
- Status: standard-of-care
- Last checked: 2026-09-04
- Principle: Loss of heterozygosity, telomeric allelic imbalance, and large-scale transitions summed into a genomic instability score.
- Strengths: Extends PARP-inhibitor benefit beyond BRCA carriers
- Limitations: Scar is permanent even after resistance emerges; Threshold debates

## Sources

- PAOLA-1: olaparib added to bevacizumab maintenance in newly diagnosed ovarian cancer, with benefit confined to HRD-positive tumours (New England Journal of Medicine 2019): https://doi.org/10.1056/NEJMoa1911361

## Connected records

- technologies: [HRD genomic scar scores (GIS, LOH, HRDetect)](https://onco.cc/technologies/hrd-genomic-scar-scores/), [RAD51 foci assay (functional HRD test)](https://onco.cc/technologies/rad51-foci-assay/), [STRIDE DNA break detection (intoDNA)](https://onco.cc/technologies/stride-dna-break-detection/)
- fronts: [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/)
- targets: [BRCA1 / BRCA2 (HRD)](https://onco.cc/targets/brca/), [PARP](https://onco.cc/targets/parp/)
- terms: [Enabling characteristic: genome instability and mutation](https://onco.cc/terms/genome-instability-mutation/), [Homologous recombination deficiency (HRD)](https://onco.cc/terms/hrd/), [Homologous recombination deficiency (HRD) in breast cancer](https://onco.cc/terms/hrd-in-breast-cancer/)
- cancers: [Ovarian cancer](https://onco.cc/cancers/ovarian/), [Pancreatic ductal adenocarcinoma](https://onco.cc/cancers/pancreatic/), [Platinum-sensitive ovarian cancer](https://onco.cc/cancers/platinum-sensitive-ovarian-cancer/), [Triple-negative breast cancer (TNBC)](https://onco.cc/cancers/tnbc/)
- key papers: [Genomic methods identify homologous recombination deficiency in pancreas adenocarcinoma and optimize treatment selection](https://onco.cc/key-papers/paper-park-hrd-pancreatic-platinum-ccr-2020/), [Homologous recombination deficiency (HRD) score predicts response to platinum-containing neoadjuvant chemotherapy in patients with triple-negative breast cancer](https://onco.cc/key-papers/paper-telli-hrd-score-platinum-tnbc-ccr-2016/), [HRDetect is a predictor of BRCA1 and BRCA2 deficiency based on mutational signatures](https://onco.cc/key-papers/paper-davies-nat-med/), [PAOLA-1: olaparib added to bevacizumab maintenance in newly diagnosed ovarian cancer, with benefit confined to HRD-positive tumours](https://onco.cc/key-papers/paper-paola-1-nejm-2019/), [Survival analysis of carboplatin added to an anthracycline/taxane-based neoadjuvant chemotherapy and HRD score as predictor of response-final results from GeparSixto](https://onco.cc/key-papers/paper-loibl-geparsixto-survival-hrd-ann-oncol-2018/), [Whole genomes redefine the mutational landscape of pancreatic cancer](https://onco.cc/key-papers/paper-waddell-whole-genomes-pancreatic-nature-2015/), [Whole-genome sequencing of triple-negative breast cancers in a population-based clinical study](https://onco.cc/key-papers/paper-staaf-tnbc-whole-genome-scan-b-nat-med-2019/)
- pathways: [DNA damage response & homologous recombination](https://onco.cc/pathways/ddr/), [Double-strand break repair: HR versus end joining](https://onco.cc/pathways/homologous-recombination-repair/), [Mutagenesis & mutational signatures](https://onco.cc/pathways/mutagenesis-signatures/), [Synthetic lethality: paired dependencies](https://onco.cc/pathways/synthetic-lethality-map/)
- people: [Isabelle Ray-Coquard](https://onco.cc/people/isabelle-ray-coquard/), [Mary-Claire King](https://onco.cc/people/mary-claire-king/), [Serena Nik-Zainal](https://onco.cc/people/serena-nik-zainal/)
- bottlenecks: [Biomarkers are not validated or standardised](https://onco.cc/bottlenecks/b-biomarker-validation/)
- ideas: [A functional test for homologous recombination deficiency validated across laboratories](https://onco.cc/ideas/idea-tr2-hrd-functional-standard/)
- institutions: [Society of Gynecologic Oncology](https://onco.cc/institutions/sgo/)
- drugs: [BRACAnalysis CDx](https://onco.cc/drugs/bracanalysis-cdx/), [myChoice CDx](https://onco.cc/drugs/mychoice-cdx/)
- companies: [ARCAGY-GINECO](https://onco.cc/companies/arcagy-gineco/), [intoDNA](https://onco.cc/companies/intodna/), [Myriad Genetics](https://onco.cc/companies/myriad-genetics/)
- roadmaps: [Diagnostics roadmap: stains → gene panels → blood tests that decide treatment](https://onco.cc/roadmaps/diagnostics-roadmap/)

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