What Is the HRD Test and Why Is It Needed? A Personalized Compass for Ovarian Cancer Treatment
In this article
The Rise of Biomarkers in Cancer Treatment
Cancer treatment has undergone a major transformation over the past twenty years. Previously, treatment approaches were determined solely by the organ in which the cancer arose ; today, the tumor's genetic and molecular signature has become the most important factor guiding treatment.
One cornerstone of personalized oncology is a biomarker called Homologous Recombination Deficiency (HRD) . HRD represents a weakness in a cancer cell's DNA repair mechanism, allowing us to predict its sensitivity to certain targeted drugs.
Understanding HRD testing is critical for individualizing treatment decisions, particularly in ovarian, breast, prostate, and pancreatic cancer . This guide explains the biological basis and clinical importance of HRD and how it shapes treatment planning, step by step.
Section 1: Cellular Defense — What Is Homologous Recombination Deficiency (HRD)?
1.1 DNA Repair: How Does the Architect of Life Work?
Every cell in our body sustains itself by continually repairing its DNA. Like a construction blueprint , DNA gives the cell all its instructions for life; preserving that blueprint intact is vital.
Cells use several mechanisms to repair DNA damage. The most sophisticated is the Homologous Recombination Repair (HRR) pathway. HRR specifically repairs double-strand DNA breaks using an intact DNA strand as a “template,” correcting damage accurately.
Genes such as BRCA1, BRCA2, RAD51, PALB2 play key roles in this process. When any of these genes fails to function, the cell cannot repair DNA damage correctly—laying the groundwork for cancer development.
1.2 How HRD Arises: Disrupted Repair Pathways and Genetic Factors
Homologous Recombination Deficiency (HRD)is the inability of a cell to use its sophisticated DNA repair mechanism. Errors accumulate in DNA, genetic stability is disrupted, and cancer development becomes easier.
- Direct Gene Mutations: The most common cause is mutations in the BRCA1 and BRCA2 genes.
- Non-BRCA Abnormalities: PALB2 and other HRR-related genes can cause HRD through mutations, as can epigenetic changes that disrupt gene expression.
HRD testing goes beyond BRCA mutations, measuring all defects in the DNA repair pathway as a “genomic scar.” This identifies patients with weak DNA repair even without a BRCA mutation—patients who may benefit greatly from targeted drugs such as PARP inhibitors.
In summary: HRD is an umbrella term encompassing all DNA repair defects beyond BRCA mutations. It allows a broader group of patients to benefit from personalized targeted therapies .
Section 2: HRD Testing — For Whom, When, and How?
HRD is one of the central biomarkers used to personalize cancer treatment as accurately as possible. By assessing cancer cells' DNA repair capacity, it predicts which patients will benefit from targeted treatments, especially PARP inhibitors. Performing the test at the right time and in the right way is critical both to treatment success and to avoiding unnecessary medication.
2.1 The Scope of HRD Testing: For Which Cancers Is It Critical?
HRD testing is particularly important in tumors where deficient DNA repair increases treatment sensitivity. In the following cancer types, HRD scoring directly influences treatment selection:
- Ovarian Cancer: The most common setting for HRD testing. It determines maintenance treatment in advanced disease.
- Breast Cancer: Particularly in the Triple-Negative Breast Cancer (TNBC) subtype, it predicts sensitivity to chemotherapy and PARP inhibitors.
- Prostate Cancer: Used to select targeted drugs in patients with treatment-resistant disease.
- Pancreatic Cancer: New research is developing combination treatments based on HRD positivity.
Scientific Note: Approximately 20% of TNBC patients have a BRCA1/2 mutation . In this group, HRD positivity significantly increases the response rate to PARP inhibitors.
2.2 The Testing Process: What Does the HRD Score Mean?
The HRD score quantitatively measures the degree of DNA repair deficiency in cancer cells. A high score indicates HRD positivity and therefore high sensitivity to PARP inhibitors .
- Tumor BRCA mutation (tBRCA): Directly indicates HRD positivity.
- Genomic scar test: For example, in the Myriad MyChoice® CDx or Genekor Rediscore® test, a score of ≥42 is considered HRD-positive.
| Cancer Type | Role of HRD Testing | Clinical Implication | Related Treatment Approach |
|---|---|---|---|
| Ovarian Cancer | Treatment response and maintenance selection | HRD-positive patients benefit greatly from PARP inhibitors | Olaparib + Bevacizumab |
| Breast Cancer (TNBC) | Personalizing treatment, predicting risk | High response in patients with BRCA mutations | PARP inhibitors, platinum-based chemotherapy |
| Prostate Cancer | Identifying targets in resistant subgroups | Identifying a treatment-sensitive subgroup | Olaparib, Rucaparib |
| Pancreatic Cancer | Emerging treatment strategies | Potential future use of PARP inhibitors | Investigational combinations |
※ Note: Niraparib monotherapy showed a PFS benefit in the overall population as first-line maintenance (PRIMA); efficacy is greater in the HRD(+) group, while use in HRD(–) disease is considered in selected cases.
2.3 Why Is Test Quality Vital? (Logistical Challenges)
HRD testing is usually performed on tumor tissue. Its success depends on timely and correct processing of the tissue sample. Pathology procedures and sample logistics must therefore be handled with great care.
- Speed After Surgery: The tissue sample should be placed in fixative within 1 hour of excision.
- Type of Fixative: 10% Neutral Buffered Formalin (NBF) is preferred.
- Fixation Duration: The optimal duration is 8–36 hours and must not exceed 72 hours.
- Processing Large Samples: Tissues should be cut before fixation to allow formalin penetration.
⚠️ Warning: If tissue is not handled correctly, DNA may deteriorate and the test may fail. This can deprive the patient of the opportunity for targeted treatment.
Section 3: The Vital Importance of HRD Positivity in Ovarian Cancer
Ovarian cancer is among the cancers in which HRD testing has the greatest influence on treatment decisions. In particular, HRD status guides the choice of post-chemotherapy maintenance treatment , determines sensitivity to PARP inhibitors , and increases the chance of long-term recurrence-free survival.
3.1 The Key to Targeted Treatment: Synthetic Lethality
Synthetic lethalityrefers to cell death when one of the two DNA repair pathways a cancer cell uses to survive is already defective (HRR), and the second pathway (PARP) is blocked by a drug.
- HRD-positive cell: The sophisticated repair pathway (HRR) is not working.
- PARP inhibitor: The alternative repair pathway also shuts down → the cell cannot repair DNA damage → it dies.
- Selectivity: Normal cells retain HRR and are therefore relatively less affected.
Practical meaning: HRD-positive tumors are markedly more sensitive to PARP inhibitors ; HRD testing is therefore a key marker for maintenance treatment selection.
3.2 Treatment Decisions in Light of Clinical Evidence
The standard approach in advanced ovarian cancer is surgery + platinum-based chemotherapy. Because recurrence risk is high, maintenance treatment is vital after successful chemotherapy. HRD testingguides this maintenance choice as a predictive biomarker.
🔎 The PAOLA-1 framework: In HRD-positive patients with newly diagnosed advanced disease, Olaparib + Bevacizumab maintenance showed a significant progression-free survival advantage.
The PRIMA trial also showed that Niraparib monotherapy provides a PFS benefit in the overall population, with greater efficacy in the HRD(+) subgroup and limited efficacy in the HRD(–) group.
| Genetic Status | HRD Status | Clinical Prediction | Possible Maintenance Approach |
|---|---|---|---|
| BRCA-mutated (germline/somatic) | Usually HRD-positive | Potential for high benefit through synthetic lethality | Single-agent PARP inhibitor (e.g., Olaparib; the SOLO framework) or Olaparib + Bevacizumab (HRD+ subgroup, PAOLA-1) |
| No BRCA mutation, HRD-positive (e.g., genomic scar ≥42) | HRR deficiency present | PARP-sensitive subgroup | Olaparib + Bevacizumab (PAOLA-1) • Niraparib monotherapy (strong benefit in HRD+ in PRIMA) |
| No BRCA mutation, HRD-negative (low score) | HRR largely preserved | Single-agent PARP: limited efficacy | Bevacizumab maintenance or close monitoring; Niraparib monotherapy (selected cases—benefit in PRIMA, but more limited than in HRD+; considering toxicity/quality of life) |
📊 Clinical Note: PAOLA-1 showed a significant PFS increase in HRD-positive patients with Olaparib + Bevacizumab . PRIMA also reported that Niraparibprovided a PFS benefit in the overall population, but efficacy in the HRD-negative subgroup was more limited . Niraparib may therefore be considered for HRD-negative patients in an individualized manner, taking patient preference, toxicity profile, and clinical context into account.
📌 Important: HRD status may strongly predict maintenance response regardless of stage or initial residual disease.
⚠️ Warning: In the HRD-negative group, single-agent PARP benefit may be limited; individualization is needed, considering toxicity profile and quality of life.
🧭 Clinical compass: HRD testing guides suitable patients toward PARP inhibitor maintenance or combinations such as Olaparib + Bevacizumab .
Section 4: Interpreting Test Results and Future Strategies
HRD test results shape not only the current treatment plan, but also familial risks and future treatment options . Correct interpretation is therefore critical for both patient and physician.
4.1 What Does the HRD Score Mean?
HRD testing quantitatively measures DNA repair deficiency in the tumor genome. This score helps predict how much a patient may benefit from treatment:
- High HRD Score (Positive): The cell cannot repair DNA damage and is highly sensitive to PARP inhibitors.
- Low HRD Score (Negative): The cell's repair capacity is largely preserved; response to PARP inhibition is low.
Clinical meaning: High HRD score = longer progression-free survival (PFS) and substantial benefit from targeted maintenance treatment.
4.2 Hereditary Risk and Genetic Counseling
When HRD positivity is detected, it is necessary to determine whether it is inherited or confined to the tumor . An inherited BRCA1/2 mutation also carries a cancer risk for family members.
- Inherited (germline) mutations: Have a 50% chance of being passed to children.
- BRCA1 mutation: Increases breast/ovarian cancer risk in women and prostate cancer risk in men.
- BRCA2 mutation: Significantly increases breast cancer risk in men.
Recommendation: If the HRD test identifies an inherited mutation, genetic counseling should be provided, and first-degree relatives should enter a screening program.
4.3 Treatment Resistance Mechanisms and Future Directions
Although HRD positivity initially predicts treatment success, some tumors may develop resistance to PARP inhibitors over time. This reflects cancer's biological adaptability.
- HRR reactivation: The tumor may regain its lost repair pathway.
- Resistance to drug entry: Entry of the PARP inhibitor into the cell may be blocked.
Research direction: New research is testing combinations of PARP inhibitors with immunotherapy or other targeted agents . The aim is to overcome resistance mechanisms and achieve lasting remission.
Section 5: Conclusion and Recommendations for Patients
Homologous Recombination Deficiency (HRD) testing has become the compass of personalized oncology in many cancers, particularly ovarian cancer. By revealing the tumor's genetic weakness, this test enables patients to receive the most effective targeted treatments.
HRD positivity provides patients treated with PARP inhibitors with significantly longer progression-free survival (PFS) and lowers recurrence risk. HRD testing is therefore a powerful example of the era of biomarker-based decision-making in modern cancer treatment.
5.1 The Value of HRD Testing: A Triumph for Individualized Treatment
HRD testing is not merely a laboratory result; it is a strategic guide to delivering the right drug to the right patient at the right time . By revealing the tumor's genetic weakness, it sharpens the treatment target.
Summary: A high HRD score is key to long-term remission that prevents disease from returning. This test has replaced “one-size-fits-all” approaches in cancer treatment with individualized strategies .
5.2 Key Takeaways and Recommendations for Patients
- Ask About HRD Testing: Patients with newly diagnosed advanced ovarian cancer should discuss HRD testing with their doctors when treatment is being planned.
- Sample Quality Is Vital: Timely fixation of surgical or biopsy samples is critical to test success.
- A Key to Treatment Access: A positive HRD result increases the likelihood of long-term recurrence-free survival with PARP inhibitors and combination maintenance treatments.
- Managing Hereditary Risk: If there is an inherited mutation in BRCA or another DNA repair gene, family members should also receive genetic counseling.
- A Dynamic Treatment Process: Cancer treatment is not static; options continue to expand through new clinical trials and combination treatments.
5.3 Looking Ahead: PARP Combinations and New Horizons
For HRD-positive cancers, researchers are exploring new-generation combinations of PARP inhibitors with immunotherapies or angiogenesis inhibitors . These strategies aim to reduce resistance and achieve more durable treatment responses .
Vision: In the oncology of the future, HRD testing will become a biological guide shaping not only treatment selection but management across the entire lifespan .
Was this article helpful?
Your feedback helps us improve our content.
Reader comments
Share your comment
Your name and comment are published only after administrator approval. Your email address is never shown to visitors.
Be the first to comment.