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HRD & HRR

Homologous Recombination Deficiency (HRD) and Homologous Recombination Repair (HRR) Testing

Overview


Homologous recombination deficiency (HRD) refers to a cell’s inability to repair DNA double-strand breaks through the homologous recombination repair (HRR) system.

This defect often results from mutations in genes like BRCA1, BRCA2, RAD51, and PALB2. HRD is associated with genomic instability, which can make tumors more sensitive to treatments such as PARP inhibitors and platinum-based chemotherapy.

Testing for HRR & HRD– Jaipur Molecular Lab
HRD testing at Jaipur Molecular Lab identifies signs of genomic instability or mutations in HRR genes. It involves:

  • HRR gene mutations (e.g., BRCA1/2)
  • Genomic instability biomarkers such as loss of heterozygosity (LOH)

Tests vary by lab and may provide an HRD score—a quantitative assessment of repair deficiencies.

Implications for Practice
HRD testing is especially relevant for ovarian, breast, pancreatic, and prostate cancers, helping guide treatment with PARP inhibitors and other DNA repair-targeting therapies. For example:

  • HRD-positive tumors are more likely to respond to PARP inhibitors, which block DNA repair pathways in cancer cells, leading to cell death.
  • HRD testing can predict responsiveness to platinum-based chemotherapy in ovarian cancer and treatment outcomes in triple-negative breast cancer.

HRD and HRR Testing Differences at Jaipur Molecular Lab

  • HRD Testing focuses on genomic instability markers and mutations causing repair defects.
  • HRR Gene Testing detects inherited (germline) and acquired (somatic) mutations in DNA repair genes, offering insights into hereditary cancer risks.

Homologous recombination DNA repair (HRR). A double-stranded DNA break and sister chromatid that will be used as a template for repair. B MRN and CtIP are involved in DNA resection. C HRR repair complex. D Schematic representation of BRCA1/2 mediated HRR

Key Findings and Applications

  • Around 50% of women with high-grade serous ovarian cancer show HRD.
  • BRCA1/2 mutations are present in 17% of ovarian cancers, and other HRR gene mutations occur in 28%.
  • HRR testing helps guide personalized therapy, including PARP inhibitors and platinum-based treatments.

Testing Methodology

  • Requires high-quality tumor samples from surgery or biopsy.
  • Detects somatic mutations; germline testing needs separate blood analysis.
  • Accurate results depend on biomarker selection and lab-specific methodologies.

Challenges and Future Directions
Standardizing HRD HRR testing is crucial as labs use different biomarkers and scoring systems, leading to variability in results. Collaborative efforts aim to establish guidelines to improve consistency, enhance clinical decision-making, and expand HRD-related therapies to more cancer types.

In summary, HRD & HRR testing at Jaipur Molecular Lab provide vital insights into tumor biology, enabling more effective treatment strategies and improving patient outcomes.