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NRG-GY019 — Letrozole monotherapy vs paclitaxel/carboplatin + letrozole in low-grade serous ovarian (frontline)

Abstract: Plenary I · Session: Friday April 10, 2026 · Simultaneous publication: TBD (Gynecologic Oncology / JCO)

Headline: The "negative" Plenary trial that nonetheless settles a long-running debate — letrozole monotherapy failed non-inferiority vs paclitaxel/carboplatin + letrozole as frontline therapy in low-grade serous ovarian cancer (LGSOC), preserving chemotherapy as the SOC backbone.

At a glance

  • Sponsor / cooperative groups: NRG Oncology (NRG-GY019)
  • PI / presenter: Amanda Fader, MD (Johns Hopkins)
  • NCT ID: NCT04095364
  • Phase / arms / N: Phase 3 randomized open-label non-inferiority; ~450 patients (letrozole alone vs paclitaxel/carboplatin + letrozole)
  • Primary endpoint(s): PFS (non-inferiority margin pre-specified)
  • Indication / line: Frontline newly diagnosed Stage II–IV low-grade serous ovarian cancer (HR+ biology)
  • Comparator: Paclitaxel + carboplatin + letrozole (chemo + endocrine SOC)
  • Session: Plenary I (Day 1, Apr 10)

Headline result

Letrozole monotherapy did not meet the pre-specified non-inferiority margin vs paclitaxel/carboplatin + letrozole. PFS favored the chemo-containing arm; the non-inferiority bound was crossed. This is a "practice-preserving" negative — the design tested whether chemotherapy could be eliminated from frontline LGSOC in favor of endocrine monotherapy, and the answer is no.

Mechanism / class

Letrozole is a non-steroidal aromatase inhibitor. LGSOC is hormone-receptor-positive (ER/PR+) in the majority of cases, motivating the endocrine-monotherapy hypothesis tested in NRG-GY019. The mechanism question — whether HR+ biology in LGSOC behaves like HR+ breast (where endocrine monotherapy can suffice in some settings) — was answered negatively.

Trial design deep dive

Study architecture: Phase 3 randomized open-label non-inferiority, 1:1 to letrozole 2.5 mg PO daily monotherapy vs paclitaxel 175 mg/m² + carboplatin AUC6 Q3W for 6 cycles followed by letrozole 2.5 mg PO daily maintenance. ~450 patients, frontline newly diagnosed Stage II–IV low-grade serous ovarian cancer post-cytoreductive surgery (R0/R1/R2 strata TBD). NRG Oncology cooperative-group execution. Stratification by stage and residual disease per protocol.

Endpoint definitions: PFS (primary) with pre-specified non-inferiority margin (specific HR boundary TBD per protocol — typically 1.3–1.4 in oncology NI designs). Failure to meet the upper-bound NI margin is what defines this as a "negative" non-inferiority trial — letrozole alone could not be declared non-inferior. Secondary endpoints include OS, ORR (in measurable disease), PRO/QoL, and tolerability — important given chemo's toxicity penalty in a chronic-biology disease.

Key subgroup analyses: KRAS-mutated subgroup (critical given RAMP-201 avutometinib + defactinib data showing PFS 19.6 mo, DOR 31 mo in KRAS-mut LGSOC) reserved for follow-up. ER/PR expression-quantitative subgroups, stage, age, and residual-disease strata pre-specified. The negative top-line does not preclude a positive endocrine-only signal in a molecularly defined subset, but no such subset was rescue-defined.

Comparator context: Paclitaxel/carboplatin + letrozole maintenance reflects pragmatic LGSOC SOC. The trial was designed to deescalate by removing chemo — the negative result preserves the chemo backbone.

FDA implications: No new approval — practice-preserving negative. Reaffirms NCCN guideline language that chemo + endocrine maintenance remains frontline SOC; future deescalation attempts will need molecular enrichment (KRAS-mut, MEK-inhibitor combination paradigm).

Discussant takeaway

Plenary I framing: NRG-GY019 closes a decade-long debate about chemo elimination in LGSOC. Combined with RAMP-201's KRAS-mut LGSOC durability (DOR 31 mo, PFS 19.6 mo in KRAS-mut), the field now has clear sequencing — chemo + letrozole remains frontline SOC; avutometinib + defactinib emerges in KRAS-mut recurrent disease.

Practice-changing verdict

Yes (negative-confirmatory). Preserves the chemo + endocrine backbone in frontline LGSOC; rules out the "letrozole alone" simplification. Important for NCCN-guideline reaffirmation of the chemo backbone in this HR+ subset.

  • Other SGO 2026: RAMP-201 follow-up (avutometinib + defactinib in KRAS-mut LGSOC, DOR 31 mo)
  • AACR 2026: MEK/FAK combination and KRAS-mut LGSOC sessions
  • ASCO 2026: Expected long-term safety + endocrine-resistance biomarker follow-up
  • Cross-tumor: HR+ breast endocrine-monotherapy paradigm (PALOMA, MONALEESA) as the analogy that did not transfer to LGSOC

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