Why PARP Inhibition and Immune Checkpoint Blockade Are Being Combined in HRD Ovarian Cancer
The scientific rationale for pairing a PARP inhibitor with a PD-1 antagonist in homologous recombination deficient (HRD) ovarian cancer rests on a mechanistic overlap: PARP inhibitors like niraparib induce DNA damage accumulation in HRD tumour cells, and that accumulation can increase tumour immunogenicity, potentially sensitising the tumour microenvironment to immune checkpoint blockade. Patent filings from TESARO Inc — now part of GSK — explicitly describe this rationale, disclosing compositions and methods for using niraparib in combination with a programmed death receptor-1 (PD-1) antagonist such as pembrolizumab or nivolumab for treating cancer.
Ovarian cancer characterised by HRD — including tumours with BRCA1 or BRCA2 mutations, as well as those with other alterations in the homologous recombination repair (HRR) pathway — has proven particularly sensitive to PARP inhibition. According to WHO cancer data, ovarian cancer remains one of the most lethal gynaecological malignancies, making first-line treatment optimisation a priority for the field. By adding pembrolizumab, which blocks the PD-1 checkpoint and restores T-cell-mediated anti-tumour immunity, the combination strategy aims to attack the tumour through two complementary mechanisms simultaneously.
TESARO Inc patents (e.g. WO2021067417A1, WO2022032093A1) disclose methods for using niraparib in combination with a PD-1 antagonist — such as pembrolizumab or nivolumab — as a first-line treatment for ovarian cancer, fallopian tube cancer, and peritoneal cancer in patients with BRCA1 mutations, BRCA2 mutations, or homologous recombination deficiency (HRD).
The combination is also being evaluated in the all-comers population — patients whose tumours are not specifically selected for HRD or BRCA mutation status — reflecting an ambition to extend the benefit of the regimen beyond the biomarker-defined subgroup. This breadth of intent is documented across multiple TESARO patent families filed between 2020 and 2024.
The Patent Landscape: TESARO’s Combination Strategy and Key Filings
TESARO Inc has filed a dense cluster of patent applications covering the niraparib and PD-1 antagonist combination, with filings spanning the United States, Europe, China, and via the PCT system — a deliberate multi-jurisdictional approach that signals the commercial importance of this combination therapy. The core combination patents (WO2021067417A1, US20220000843A1, US20220273654A1, WO2022032093A1, CN115605226A, CN117695396A) share a common disclosure: compositions and methods for administering niraparib with an anti-PD-1 antibody, with pembrolizumab as the primary named agent, for first-line treatment of ovarian, fallopian tube, and peritoneal cancers.
A separate but related family covers monitoring of PARP inhibitor and immune checkpoint inhibitor treatment (WO2023004353A1), disclosing methods for detecting biomarkers — including circulating tumour DNA (ctDNA) and immune biomarkers — in patient samples during the course of niraparib and/or pembrolizumab treatment. This monitoring patent signals that TESARO is building IP around the full treatment management cycle, not just the drug combination itself.
A programmed death receptor-1 (PD-1) antagonist is an antibody that blocks the PD-1 receptor on T cells, preventing cancer cells from using the PD-1/PD-L1 axis to suppress immune responses. Pembrolizumab (Keytruda) and nivolumab are both named as PD-1 antagonists in TESARO’s niraparib combination patent disclosures. By blocking PD-1, these agents restore the ability of T cells to recognise and attack tumour cells.
The niraparib formulation patents (US20230210855A1, EP3777883A1, CN113993535A) provide a further layer of protection, covering the specific dose formulations tied to the individualised dosing strategy. Together, the portfolio creates overlapping layers of protection: composition, method of use, dosing regimen, combination partner, treatment monitoring, and biomarker selection.
The FIRST Study: Phase 3 Evidence and What the Patent Record Reveals
The FIRST study is a Phase 3 clinical trial that directly compares niraparib in combination with pembrolizumab against niraparib monotherapy as a first-line treatment for ovarian cancer, fallopian tube cancer, or peritoneal cancer, administered after a platinum-based chemotherapy regimen. Patent WO2022040537A1, filed by TESARO Inc in February 2022, is the most explicit clinical-trial-linked filing in the portfolio, explicitly referencing Phase 3 clinical trial data from the FIRST study.
“The FIRST study evaluates niraparib in combination with pembrolizumab versus niraparib monotherapy — a head-to-head design that tests whether adding PD-1 blockade to an already-approved PARP inhibitor regimen delivers meaningful additional benefit in HRD-positive ovarian cancer.”
The study design covers three patient populations: those with HRD-positive cancer (including BRCA-mutated and non-BRCA HRD tumours), those with BRCA-mutated cancer specifically, and the overall all-comers population. This three-tier stratification is significant because it mirrors the way regulators have historically evaluated PARP inhibitor approvals — starting with BRCA-mutated patients, then expanding to HRD-positive patients, and ultimately seeking to demonstrate benefit in unselected populations. According to EMA guidance on oncology drug development, biomarker-stratified trial designs of this type are increasingly required for label expansions in precision oncology.
The Phase 3 FIRST study, referenced in TESARO patent WO2022040537A1, evaluates niraparib combined with pembrolizumab versus niraparib monotherapy as a first-line treatment for ovarian cancer, fallopian tube cancer, or peritoneal cancer following platinum-based chemotherapy, with pre-specified analyses in HRD-positive, BRCA-mutated, and all-comers patient populations.
Explore the full niraparib + pembrolizumab patent landscape in PatSnap Eureka — including filing timelines, claim scope, and competitive intelligence.
Explore Patent Data in PatSnap Eureka →The patent record also documents that niraparib is to be administered using an individualised dosing strategy (IDS) within the FIRST study context — a detail that connects the clinical trial design directly to the formulation and dosing IP. This integration of IDS into the combination regimen is a strategic choice: it addresses the known haematological toxicity profile of niraparib by tailoring the starting dose to patient characteristics, potentially improving tolerability in the combination setting.
Individualised Dosing, Biomarker Selection, and Treatment Monitoring
The individualised dosing strategy (IDS) for niraparib is one of the most carefully protected aspects of the portfolio. Multiple patent families — including WO2021119236A1, US20230210855A1, EP3777883A1, and CN113993535A — cover the same core principle: dosing niraparib at 200 mg daily for patients with a body weight below 77 kg and/or a baseline platelet count below 150,000/μL, and at 300 mg daily for patients with a body weight of at least 77 kg and a baseline platelet count of at least 150,000/μL. This weight- and platelet-based dosing approach was developed to reduce the incidence of thrombocytopenia, a dose-limiting toxicity of niraparib, without compromising efficacy.
Niraparib individualised dosing strategy (IDS) patents (including WO2021119236A1 and US20230210855A1 from TESARO Inc) specify 200 mg daily for patients with body weight below 77 kg and/or baseline platelet count below 150,000/μL, and 300 mg daily for patients with body weight at least 77 kg and baseline platelet count at least 150,000/μL.
On the biomarker side, Merck Sharp & Dohme LLC — Merck’s research arm and the developer of pembrolizumab — has filed its own patent (WO2024145378A1, published July 2024) specifically addressing biomarkers for pembrolizumab-based therapies in advanced ovarian cancer. This filing discloses methods for administering pembrolizumab to patients whose tumours express PD-L1 at a combined positive score (CPS) of 1 or greater, and for predicting treatment effectiveness based on PD-L1 status. The patent also covers the combination of pembrolizumab with a PARP inhibitor such as niraparib — a direct overlap with TESARO’s portfolio that reflects the collaborative yet separately protected nature of the niraparib/pembrolizumab development programme, as noted by FDA biomarker guidance frameworks for oncology co-development.
The niraparib + pembrolizumab programme is supported by two distinct biomarker frameworks: HRD/BRCA status (for PARP inhibitor sensitivity, covered in TESARO patents) and PD-L1 combined positive score ≥1 (for pembrolizumab response prediction, covered in Merck Sharp & Dohme patent WO2024145378A1). Together, these define a dual-biomarker selection strategy for the combination regimen.
The monitoring dimension of the programme is covered by TESARO patent WO2023004353A1, which describes using liquid biopsy biomarkers — specifically circulating tumour DNA (ctDNA) — as well as immune biomarkers to monitor both efficacy and toxicity during treatment with niraparib and/or pembrolizumab. This positions the combination programme within the broader trend towards real-time treatment monitoring in oncology, a direction that aligns with guidance from organisations such as ESMO on liquid biopsy use in clinical practice.
Competitive IP Signals: Merck, BeiGene, and the Broader PARP/IO Field
The PARP inhibitor and immune checkpoint inhibitor combination space is not exclusively occupied by GSK and Merck. BeiGene Ltd has filed US20240091234A1, disclosing methods for treating cancer with its own PARP inhibitor, pamiparib, in combination with an anti-PD-1 or anti-PD-L1 antibody. BeiGene’s filing targets a different set of indications — including glioblastoma, triple-negative breast cancer, non-small cell lung cancer, gastric cancer, oesophageal cancer, hepatocellular carcinoma, and microsatellite instability-high cancers — rather than ovarian cancer specifically. This divergence in indication strategy suggests that different companies are pursuing different tumour types within the PARP/IO combination space, with TESARO/GSK maintaining a concentrated focus on gynaecological cancers.
BeiGene Ltd patent US20240091234A1 (published March 2024) discloses methods for treating cancer using the PARP inhibitor pamiparib in combination with an anti-PD-1 or anti-PD-L1 antibody, targeting indications including glioblastoma, triple-negative breast cancer, non-small cell lung cancer, gastric cancer, and microsatellite instability-high cancers — distinct from TESARO’s gynaecological cancer focus.
Regeneron Pharmaceuticals has also filed in the anti-PD-1 space (WO2020264389A1) for cemiplimab in cervical cancer, endometrial cancer, non-small cell lung cancer, basal cell carcinoma, and bladder cancer — again distinct from the ovarian cancer indication. The competitive picture that emerges is one of relative white space for TESARO/GSK in HRD ovarian cancer specifically: while PARP/IO combinations are being pursued broadly, the specific niraparib + pembrolizumab + HRD ovarian cancer combination remains dominated by the TESARO patent estate.
Map the full competitive PARP/IO patent landscape — including BeiGene, Merck, Regeneron, and GSK — with PatSnap Eureka’s AI-powered analysis tools.
Analyse Competitive IP in PatSnap Eureka →The Merck Sharp & Dohme biomarker patent (WO2024145378A1) is the most recent filing in the dataset, published in July 2024, and its focus on PD-L1 CPS ≥1 as a predictive biomarker for pembrolizumab-based therapy in advanced ovarian cancer represents a forward-looking attempt to define the patient population most likely to benefit from the combination. This type of companion diagnostic-adjacent patent filing is consistent with the approach that has been adopted across pharmaceutical innovation intelligence tracking in the precision oncology sector, where biomarker IP is increasingly recognised as a critical component of the commercial strategy for combination therapies. PatSnap’s broader life sciences intelligence platform documents this trend across multiple therapeutic areas.
For IP strategists and R&D leaders monitoring this space, the key signals from the patent record are: TESARO/GSK holds a multi-layered, multi-jurisdictional patent estate covering the niraparib + pembrolizumab combination for HRD ovarian cancer; Merck Sharp & Dohme is independently protecting the pembrolizumab biomarker dimension; and the broader PARP/IO field is expanding into additional indications and PARP inhibitor molecules, but has not yet converged on the specific ovarian cancer niche with the same density of filings as the TESARO portfolio.