New England Journal of Medicine SEPTEMBER 28, 2019

Niraparib in Patients with Newly Diagnosed Advanced Ovarian Cancer (PRIMA Trial)

Antonio González-Martín, Bhavana Pothuri, Ignace Vergote, et al.

Bottom Line

The PRIMA phase III trial established that maintenance therapy with the PARP inhibitor niraparib significantly prolongs progression-free survival in newly diagnosed advanced ovarian cancer patients following a response to platinum-based chemotherapy, regardless of biomarker status, though it provides no overall survival benefit.

Key Findings

1. In the overall intent-to-treat population, niraparib significantly reduced the risk of disease progression or death compared to placebo (HR 0.62; P < 0.0001) in the primary analysis.

2. Patients with homologous recombination-deficient (HRd) tumors experienced a robust progression-free survival benefit with niraparib (median 21.9 months vs. 10.4 months; HR 0.43; P < 0.0001).

3. Final overall survival analysis after approximately 6 years of follow-up showed no statistically significant difference between niraparib and placebo in the overall population (median OS 46.6 vs. 48.8 months; HR 1.01; P = 0.8834).

4. Long-term outcomes demonstrated sustained efficacy, with 5-year progression-free survival rates favoring niraparib (22% vs. 12% in the overall population; 35% vs. 16% in the HRd subgroup).

5. The safety profile remained consistent with established data for niraparib, with no new safety signals observed in long-term follow-up; incidences of secondary malignancies such as myelodysplastic syndromes/acute myeloid leukemia remained low (<2.5%).

Study Design

Design

RCT

Double-Blind

Sample

733

Patients

Duration

73.9 mo

Median

Setting

Multicenter, International

Population Patients with newly diagnosed, advanced (stage III or IV) high-grade serous or endometrioid ovarian, fallopian tube, or primary peritoneal cancer who achieved a complete or partial response to first-line platinum-based chemotherapy.

Intervention Oral niraparib 300 mg once daily (or individualized dose) for up to 36 months.

Comparator Matched placebo once daily for up to 36 months.

Outcome Progression-free survival (PFS) by blinded independent central review, evaluated hierarchically in the homologous recombination-deficient (HRd) population first, then the overall population.

Study Limitations

• The trial exclusively enrolled patients at high risk of recurrence, specifically those with stage III disease who had residual disease after surgery or stage IV disease, limiting the generalizability to patients with no visible residual disease.

• The initial fixed-dose regimen (300 mg daily) resulted in frequent adverse events, necessitating a subsequent protocol amendment for individualized dosing based on weight and platelet count.

• The trial was not powered to detect small differences in overall survival, and the high rate of subsequent therapy (including other PARP inhibitors) in the placebo arm may have confounded long-term survival assessments.

• The study population was predominantly white (89%), which may limit the applicability of the findings across more diverse ethnic groups.

Clinical Significance

Niraparib is established as a standard first-line maintenance option for patients with advanced ovarian cancer who respond to platinum-based chemotherapy, offering a durable progression-free survival benefit. While it does not improve overall survival, the substantial delay in time to subsequent treatment and sustained progression-free benefit in the HRd population support its continued clinical utility.

Historical Context

At the time of the PRIMA trial, PARP inhibitors were primarily approved for the recurrent setting. PRIMA was pivotal in expanding the use of PARP inhibitors to the first-line maintenance setting, serving as the landmark study that demonstrated efficacy beyond just BRCA-mutated patients, effectively including those with broader HRd and HR-proficient status.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

What is the concept of 'synthetic lethality' and how does it explain the mechanism of action for niraparib in patients with BRCA mutations?

Key Response

Synthetic lethality occurs when the simultaneous loss of two genes or pathways leads to cell death, while the loss of either alone does not. In BRCA-mutated cells, the homologous recombination repair (HRR) pathway for double-strand DNA breaks is already defective. Niraparib inhibits Poly(ADP-ribose) polymerase (PARP), which is essential for repairing single-strand breaks via base excision repair. The combination of these two defects leads to an accumulation of unrepaired DNA damage and subsequent apoptosis of the cancer cells.

Resident

The PRIMA trial utilized an 'individualized starting dose' (ISD) of niraparib. How does this protocol adjustment affect clinical management and what criteria determine the dose?

Key Response

To mitigate high rates of grade 3/4 thrombocytopenia observed in earlier trials, the PRIMA trial implemented an ISD based on the patient's baseline body weight and platelet count. Patients weighing <77 kg or with a baseline platelet count <150,000/μL started at 200 mg daily, while others started at 300 mg. This approach significantly improved the safety profile and reduced dose interruptions without compromising the efficacy of the maintenance therapy.

Fellow

How do the outcomes of the HRD-proficient (HRP) subgroup in the PRIMA trial influence the decision between niraparib maintenance and a 'watch-and-wait' approach in the first-line setting?

Key Response

While the PRIMA trial showed a statistically significant benefit in the HRP population (Hazard Ratio 0.68), the absolute median PFS benefit was relatively modest (8.1 vs. 5.4 months). A fellow must weigh this 2.7-month extension against the potential for long-term toxicities, such as myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML), and the impact on quality of life, as the trial did not demonstrate a significant overall survival benefit in this specific subgroup.

Attending

In light of the PRIMA trial and the lack of demonstrated overall survival (OS) benefit, how should a clinician integrate the risk of secondary malignancies into the shared decision-making process for maintenance therapy?

Key Response

Despite the impressive PFS hazard ratios, long-term follow-up across PARP inhibitor trials (including PRIMA) has raised concerns about the small but cumulative risk of secondary myeloid malignancies (MDS/AML), particularly in patients with germline mutations or extensive prior platinum exposure. The attending should emphasize that maintenance therapy optimizes the 'first-line interval,' which is often the most critical window for cure or long-term remission, but the risk-benefit ratio becomes more nuanced in HRP patients where the PFS gain is narrower.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

Critique the use of 'Progression-Free Survival' as the primary endpoint in the PRIMA trial considering the subsequent availability of PARP inhibitors in later lines of therapy.

Key Response

PFS is often used in ovarian cancer trials because it is reached faster than OS and is not confounded by subsequent treatments. However, if patients in the placebo arm 'cross over' to receive a PARP inhibitor upon recurrence, the potential OS benefit of using the drug in the first-line maintenance setting may be obscured. This makes it difficult to determine if early exposure to niraparib is superior to sequential use, necessitating complex statistical modeling like Rank Preserving Structural Failure Time (RPSFT) to estimate the true survival impact.

Journal Editor

The PRIMA trial reports a significant benefit in the 'overall population.' To what extent does the magnitude of effect in the HRD-deficient subgroup drive this result, and does the study design sufficiently power the HRD-proficient cohort to stand as a localized finding?

Key Response

A rigorous reviewer would flag the hierarchical testing strategy. Because the trial tested the HRD-deficient group first and then the overall population (which includes the HRD-deficient group), the 'overall' success is heavily weighted by the massive benefit seen in the HRD+ patients. Editors look for subgroup analyses that are pre-specified and sufficiently powered to ensure that recommendations for 'all-comers' do not inadvertently generalize a benefit to a subgroup where the effect size is clinically negligible or lacks statistical independence.

Guideline Committee

Based on the PRIMA results, how should current guidelines (e.g., NCCN or ESMO) differentiate the recommendation for niraparib in HRP versus HRD-deficient patients?

Key Response

Current NCCN guidelines list niraparib as a Category 1 recommendation for first-line maintenance in all-comers who respond to platinum. However, the committee must specify that the magnitude of benefit is highest in BRCA-mutated and HRD-positive patients. For HRP patients, the guidelines should reflect a 'may be considered' or nuanced recommendation, noting the 0.68 HR but smaller absolute PFS gain, ensuring clinicians prioritize biomarker testing to set realistic expectations for therapy duration and response.

Clinical Landscape

Noteworthy Related Trials

2016

NOVA Trial

n = 553 · NEJM

Tested

Niraparib

Population

Recurrent ovarian cancer

Comparator

Placebo

Endpoint

Progression-free survival

Key result: Niraparib maintenance therapy significantly improved progression-free survival in patients with platinum-sensitive recurrent ovarian cancer, regardless of BRCA mutation status.

2018

SOLO-1 Trial

n = 391 · NEJM

Tested

Olaparib

Population

Newly diagnosed advanced ovarian cancer with BRCA mutation

Comparator

Placebo

Endpoint

Progression-free survival

Key result: Olaparib maintenance therapy provided a significant progression-free survival benefit in patients with BRCA-mutated advanced ovarian cancer.

2019

PAOLA-1 Trial

n = 806 · NEJM

Tested

Olaparib plus bevacizumab

Population

Newly diagnosed advanced ovarian cancer

Comparator

Placebo plus bevacizumab

Endpoint

Progression-free survival

Key result: The addition of olaparib to bevacizumab maintenance significantly extended progression-free survival in patients with advanced ovarian cancer, particularly those with homologous recombination deficiency.

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