Ovarian Cancer Trial Design Patterns
Definition
Ovarian cancer encompasses epithelial ovarian cancer (EOC, ~90%), fallopian tube cancer, and primary peritoneal cancer — treated as a unified entity in clinical trials. Phase 3 ovarian cancer trials are stratified by: BRCA1/2 mutation status (germline and/or somatic), homologous recombination deficiency (HRD) status (BRCA-mutant + HRD-positive non-BRCA), platinum sensitivity (platinum-sensitive relapse: progression >6 months after last platinum; platinum-resistant: ≤6 months), and residual disease after debulking surgery.
CTG Phase 3 ovarian dataset (230 trials): PFS primary 76/230 (33%), OS primary ~40/230 (17%), ORR primary ~25/230 (11%). Median enrollment ~400 patients.
Key response criteria: RECIST 1.1 for CT-assessable disease; GCIG CA-125 criteria (≥2× baseline CA-125 on two measurements ≥1 week apart) can supplement RECIST for biochemical progression. Composite PFS (RECIST progression OR CA-125 progression OR death) used in some designs.
Regulatory Position
First-line maintenance: PFS is the standard primary endpoint for first-line maintenance trials (PARP inhibitors: SOLO-1, PRIMA, PAOLA-1). OS is key secondary; given active subsequent therapy and long post-progression survival (5–10 years), OS maturity requires 10+ years of follow-up.
Platinum-sensitive relapse maintenance: PFS primary (SOLO-2, STUDY-19). OS eventually demonstrated for some PARP inhibitors.
Platinum-resistant relapse: ORR primary for accelerated approval; PFS or OS for regular approval. Active agents have modest ORR (15–25%) in this setting.
FDA position: PFS is accepted as the primary endpoint for ovarian cancer maintenance/treatment trials given the well-established correlation between PFS prolongation and OS benefit in this disease. Large PFS HRs (0.30–0.50 in BRCA-mutant populations) support approval.
Status: FDA Cancer Endpoints 2018 = Final
When to Use Each Endpoint
| Setting | Primary Endpoint | Key Secondary | Notes |
|---|---|---|---|
| 1L treatment (chemotherapy +/- bevacizumab) | OS | PFS, ORR | GOG-0218 (bev, PFS HR 0.72; OS HR 0.89 — NS) |
| 1L maintenance (PARP inhibitor, BRCA-mutant) | PFS | OS, CA-125 response | SOLO-1 (olaparib, PFS HR 0.30) |
| 1L maintenance (PARP inhibitor, HRD+) | PFS | OS | PRIMA (niraparib, PFS HR 0.43 HRD+); PAOLA-1 (olaparib+bev, HR 0.33 BRCA-mutant) |
| 1L maintenance (all-comers, limited HRD benefit) | PFS | OS | VELIA (veliparib — negative in non-BRCA); ATHENA |
| Platinum-sensitive relapse treatment | PFS | OS, ORR | STUDY-10 (olaparib maintenance, PFS HR 0.35 BRCA-mutant) |
| Platinum-sensitive relapse maintenance | PFS | OS | SOLO-2 (olaparib, PFS HR 0.30); NOVA (niraparib, HR 0.27 germline BRCA) |
| Platinum-resistant relapse | ORR | PFS, OS | Bevacizumab (AURELIA), single-agent chemotherapy |
| Recurrent (all-comers) | PFS or OS | ORR | ICON6 (cediranib, PFS HR 0.56) |
Design Considerations
BRCA-Stratified Hierarchical Testing
Modern ovarian cancer Phase 3 designs use hierarchical testing across biomarker populations:
Primary: PFS in BRCA-mutant (α = 0.05) → if significant →
Sequential: PFS in HRD-positive (BRCA + non-BRCA HRD) → if significant →
Sequential: PFS in all-comers (ITT)
This gatekeeping approach ensures Type I error control while testing benefit in progressively broader populations. PARP inhibitors have largest benefit in BRCA-mutant, modest in non-BRCA HRD, minimal or absent in HRD-negative.
BRCA and HRD testing requirements:
- Germline BRCA: FDA-approved CDx (BRACAnalysis CDx, FoundationOne CDx for somatic)
- HRD score: myChoice CDx (Myriad Genetics) — HRD positive defined as BRCA1/2 mutation OR genomic instability score ≥42
- Central testing preferred for registrational trials; retrospective BRCA assignment from archival tissue acceptable for some secondary analyses
PFS Definition in Ovarian Cancer
Ovarian PFS is often defined as a composite of RECIST + CA-125 + death:
- RECIST 1.1 progression: Standard for CT-measurable disease
- CA-125 progression (GCIG criteria): For patients without measurable disease at baseline; or as confirmatory evidence of progression
- Death from any cause: Composite component (counts as PFS event)
Pre-specification required: Protocol must specify whether PFS is RECIST-only, RECIST+CA-125 composite, or CA-125 confirmatory. Different definitions produce different PFS HRs and event rates.
IRC requirement: Open-label ovarian cancer trials require central radiologic review. CA-125 progression adjudication may require central laboratory.
Platinum-Rechallenge as IE
In platinum-sensitive relapse trials, protocol-specified platinum rechallenge is part of the treatment strategy (not an IE). However, in maintenance trials, initiation of platinum-based therapy post-maintenance is a clinical outcome:
- Maintenance trial PFS: Event-driven by RECIST/CA-125 progression — platinum rechallenge timing is post-PFS event
- Not an IE for PFS: Rechallenge happens after progression is documented
Time to Second Progression (PFS2)
Emerging secondary endpoint: time from randomization to second progression or death. Captures whether first-line maintenance benefit extends to the second treatment line:
- No FDA formal guidance on PFS2 estimand
- Composite strategy (second progression or death) — analogous to PFS
- Sensitive to timing of rechallenge and the second-line treatment chosen
Intercurrent Events
Subsequent Platinum Rechallenge (Treatment Policy for OS)
- OS: Treatment policy — all deaths counted regardless of subsequent platinum regimens, PARP inhibitors, bevacizumab, or experimental agents
- 5+ lines of therapy typical in ovarian cancer; hypothetical OS would require censoring the majority of the dataset
- SOLO-1 long-term follow-up: OS HR 0.55 (at median 7.4 years follow-up) — treatment policy ITT
Early Discontinuation for PARP Inhibitor Toxicity
- Hematologic toxicity (cytopenias) causes dose interruptions/reductions in ~30–40% of patients receiving niraparib or olaparib
- Treatment policy: Continue PFS assessments after dose reduction; events counted regardless
- Dose reduction is the standard management strategy; per-protocol dose reductions are part of the treatment policy
Death Without Documented Radiologic Progression (Composite)
Some ovarian cancer patients die of treatment complications or cancer without formal RECIST documentation of progression. Composite strategy: death is a PFS event regardless of last tumor assessment status.
SAP language: "Death from any cause will be considered a PFS event regardless of the patient's last tumor assessment status. Death without prior documented disease progression will be counted as a PFS event dated to the date of death."
Regulatory Precedent
| Trial | Drug | Setting | Primary Endpoint | HR / Result | Approval |
|---|---|---|---|---|---|
| SOLO-1 | Olaparib maintenance | 1L BRCA-mutant | PFS | HR 0.30 (7-year PFS 67% vs 50%) | Regular (2018) |
| PRIMA | Niraparib maintenance | 1L HRD+ | PFS | HR 0.43 (HRD+); HR 0.62 (all-comers) | Regular (2020) |
| PAOLA-1 | Olaparib + bevacizumab | 1L maintenance | PFS | HR 0.33 (BRCA-mutant); HR 0.59 (HRD+) | Regular (2020) |
| SOLO-2 | Olaparib maintenance | Platinum-sensitive relapse BRCA-mutant | PFS | HR 0.30 | Regular (2017) |
| NOVA | Niraparib maintenance | Platinum-sensitive relapse | PFS | HR 0.27 (germline BRCA) | Regular (2017) |
| STUDY-19 | Olaparib maintenance | Platinum-sensitive relapse (enriched BRCA) | PFS | HR 0.35 | Accelerated → Regular |
| GOG-0218 | Bevacizumab + carboplatin/paclitaxel | 1L treatment | PFS | HR 0.72 | Regular (2018, restricted to Stage III-IV) |
| AURELIA | Bevacizumab + chemo | Platinum-resistant relapse | PFS | HR 0.48 | Regular (2014) |
Limitations and Pitfalls
OS immaturity at PFS primary analysis: With 5–10 year post-progression survival, OS follow-up of 10+ years is required in 1L maintenance trials. PFS primary is regulatory necessity, not scientific preference. Long-term OS data are now emerging (SOLO-1: OS HR 0.55 at 7.4 years).
HRD testing heterogeneity: Multiple HRD assays (myChoice, FoundationOne, internal platforms) with different cutpoints. Cross-trial HRD comparisons unreliable. FDA has not standardized HRD testing requirements beyond CDx co-development for specific approvals.
Benefit in HRD-negative (all-comers) patients: PARP inhibitor benefit is minimal or absent in HRD-negative tumors (BRCA-wildtype, HRD-negative). Approvals in all-comers populations (niraparib PRIMA) are driven by HRD+ subgroup; HRD-negative patients derive little benefit. Labeling must clearly distinguish subgroup benefits.
PFS2 without FDA guidance: Reporting PFS2 as a secondary endpoint without clear estimand specification creates interpretability problems. No SAP template established.
CA-125-only progression: CA-125 rise without radiologic progression may lead to treatment discontinuation before RECIST confirmation — protocol must specify whether CA-125-only progression counts as a PFS event or triggers additional imaging.
Backlinks
- Oncology Endpoint Overview
- Progression-Free Survival (PFS)
- Multiple Endpoints and Alpha Allocation
- Intercurrent Events in Oncology Trials
Source: FDA Cancer Endpoints 2018 (Final); GCIG CA-125 response criteria Compiled from FDA guidance + CTG Phase 3 ovarian dataset (230 trials) + known Phase 3 trial results