Oncology · Medical Literature
Poly(adenosine diphosphate-ribose) polymerase inhibitor maintenance therapy with niraparib in patients with primary advanced or recurrent endometrial cancer receiving dostarlimab plus chemotherapy.
Abstract
Dostarlimab+carboplatin-paclitaxel followed by dostarlimab maintenance demonstrated statistically significant and clinically meaningful benefits in progression-free and overall survival in the overall population of primary advanced/recurrent endometrial cancer versus chemotherapy alone in Part 1 of the phase 3 ENGOT-EN6-NSGO/GOG-3031/RUBY trial (NCT03981796). Part 2 evaluated the efficacy and safety of the addition of the poly(adenosine diphosphate-ribose) polymerase inhibitor niraparib to dostarlimab maintenance following dostarlimab+chemotherapy versus placebo maintenance following placebo+chemotherapy in primary advanced/recurrent endometrial cancer. Patients were randomized 2:1 to dostarlimab+chemotherapy followed by niraparib+dostarlimab maintenance (niraparib+dostarlimab arm) or placebo+chemotherapy followed by placebo maintenance (control arm). Primary endpoint was progression-free survival in the overall and mismatch repair-proficient/micro-satellite stable populations. Overall survival (key secondary endpoint) and safety were assessed. In total, 291 patients were randomized (192 to niraparib+dostarlimab; 99 to control). With approximately 22 months of follow-up, the risk of progression or death was significantly reduced by 40% (hazard ratio 0.60, 95% confidence interval 0.43 to 0.82, p <.001) and 37% (hazard ratio 0.63, 95% confidence interval 0.44 to 0.91, p =.006) with niraparib+dostarlimab versus the control in the overall and mismatch repair-proficient/micro-satellite stable populations, respectively. At 36.2 months of follow-up, no overall survival benefit was observed with niraparib+dostarlimab versus the control (hazard ratio 1.2, 95% confidence interval 0.81 to 1.78). Grade ≥3 treatment-related adverse events occurred in 70.7% of patients in the niraparib+dostarlimab arm and 37.5% in the control arm; serious treatment-related adverse events occurred in 24.6% and 9.4%, respectively. Discontinuations due to adverse events occurred in 38.7% of patients in the niraparib+dostarlimab arm and 11.5% in the control arm. While the addition of niraparib to dostarlimab maintenance showed a significant improvement in progression-free survival, there was no observed overall survival benefit. Dostarlimab+carboplatin-paclitaxel followed by dostarlimab maintenance remains the only regimen to demonstrate significant overall survival benefit versus carboplatin-paclitaxel alone in primary advanced/recurrent endometrial cancer.
Clinical relevance
In patients with primary advanced or recurrent endometrial cancer, does the addition of niraparib (a PARP inhibitor) to dostarlimab maintenance therapy, following dostarlimab plus carboplatin-paclitaxel induction, improve progression-free or overall survival compared with placebo plus chemotherapy alone? __SNAPSHOT__ {"studyDesign":"Phase 3, randomized, double-blind, multicenter, placebo-controlled trial (Part 2 of ENGOT-EN6-NSGO/GOG-3031/RUBY; NCT03981796)","setting":"Multicenter, international; specific countries not reported in available abstract","sampleSize":"n=291 (niraparib+dostarlimab arm: n=192; control arm: n=99); randomized 2:1","population":"Adults with primary advanced (stage III–IV) or first-recurrent endometrial cancer, inclusive of all MMR/MSS statuses (approximately 74.2% pMMR/MSS, 25% dMMR/MSI-H); carcinosarcoma and serous histologies included","intervention":"Dostarlimab 500 mg IV q3w + carboplatin (AUC 5) + paclitaxel 175 mg/m² q3w for 6 cycles, followed by dostarlimab 1000 mg IV q6w + niraparib 200–300 mg orally daily (weight/platelet-based dosing) for up to 3 years","comparator":"Placebo IV q3w + carboplatin + paclitaxel q3w for 6 cycles, followed by dual placebo maintenance for up to 3 years","primaryOutcome":"Investigator-assessed progression-free survival (PFS) per RECIST v1.1 in the overall population and in the pMMR/MSS subpopulation","followUp":"Approximately 22 months (median) for primary PFS analysis; 36.2 months for overall survival analysis","fundingSource":"Industry (Tesaro Inc., a GSK Group company)"}
Key findings
The trial met its co-primary endpoint of PFS in both the overall and pMMR/MSS populations. In the overall population (median follow-up ~22 months; PFS maturity 56.4%), median PFS was 14.5 months (95% CI 11.8–17.4) with niraparib+dostarlimab versus 8.3 months (95% CI 7.6–9.8) with placebo-chemotherapy — an absolute improvement of 6.2 months — corresponding to a 40% reduction in the risk of progression or death (HR 0.60; 95% CI 0.43–0.82; p<0.001). The 12-month PFS rate was 57.0% versus 33.7%, respectively. In the pMMR/MSS subpopulation (median follow-up ~22 months; PFS maturity 61.1%), median PFS was 14.3 months (95% CI 9.7–16.9) versus 8.3 months (95% CI 7.6–9.8), an absolute difference of 6.0 months, with a 37% reduction in the risk of progression or death (HR 0.63; 95% CI 0.44–0.91; p=0.006); 12-month PFS rates were 54.7% versus 31.1%. In the dMMR/MSI-H subgroup (PFS maturity 42.7%), median PFS was not evaluable versus 7.9 months (HR 0.48; 95% CI 0.24–0.96; p=0.017). NNT for PFS benefit at 12 months in the overall population: approximately 4.3 patients (calculated) [1/(0.570−0.337)]. Critically, at 36.2 months of follow-up, no overall survival benefit was observed (HR 1.2; 95% CI 0.81–1.78; OS data reported as assessed at a later data cut). Grade ≥3 treatment-related adverse events (TRAEs) occurred in 70.7% of the niraparib+dostarlimab arm versus 37.5% of controls; serious TRAEs in 24.6% versus 9.4%, respectively. Discontinuations due to adverse events were markedly higher in the experimental arm (38.7% vs. 11.5%). The most common grade ≥3 TRAEs were anemia, neutropenia, and thrombocytopenia; no treatment-related deaths were reported.
Practice implications
RUBY Part 2 establishes that the addition of niraparib to dostarlimab maintenance, following dostarlimab-based induction chemotherapy, produces a statistically significant and clinically meaningful improvement in PFS versus chemotherapy-placebo alone — an effect seen across MMR subgroups including the historically treatment-resistant pMMR/MSS population. However, this study did NOT establish an overall survival benefit: with 36.2 months of follow-up, the OS HR was 1.2 (95% CI 0.81–1.78), directionally unfavorable and without statistical significance. The authors themselves conclude that the data do not support adding a PARP inhibitor to immunotherapy maintenance in endometrial cancer. A critical interpretive limitation is that the comparator was chemotherapy-placebo alone, not dostarlimab monotherapy maintenance (which is already established as standard of care from RUBY Part 1 and has demonstrated OS benefit). Therefore, the trial does not answer whether niraparib adds benefit on top of dostarlimab maintenance alone — the clinically relevant question in current practice. Furthermore, the high rate of grade ≥3 TRAEs (70.7%) and discontinuations (38.7%) in the experimental arm raise important concerns about toxicity burden relative to a PFS-only benefit with a numerically adverse OS trend. Results may not generalize to patients who have already received immunotherapy or those with specific molecular subtypes (e.g., POLE-mutant), who were not analyzed separately. Only an abstract and secondary source reporting are available for the full publication; complete subgroup data, health-related quality of life, and time-to-second-progression outcomes were not available for this review. __LIMITATIONS__ The control arm was chemotherapy-placebo, not dostarlimab monotherapy maintenance; the study therefore cannot determine whether niraparib adds benefit on top of the already-established dostarlimab maintenance standard of care from RUBY Part 1.,The key secondary endpoint of overall survival showed no benefit and a numerically adverse HR (1.2; 95% CI 0.81–1.78), rendering the clinical relevance of the PFS improvement uncertain.,OS data maturity and follow-up duration (36.2 months) may be insufficient to detect a late survival signal, but the current data do not support benefit.,High rate of grade ≥3 TRAEs (70.7%) and discontinuations (38.7%) in the experimental arm raise concern that toxicity may offset PFS benefit, especially without an OS advantage.,Industry sponsorship (GSK/Tesaro) introduces potential for bias in design, analysis, and reporting.,Only abstract-level and conference/press-release data were available for portions of this review; full published subgroup analyses, BICR-assessed PFS, quality-of-life, and time-to-second-progression outcomes have not been fully assessed.,The trial was not powered to detect OS differences within individual molecular subgroups (e.g., pMMR/MSS, dMMR/MSI-H, POLE-mutant).,Generalizability is limited: patients eligible for first-line therapy for primary advanced or first recurrent disease; those with prior immunotherapy exposure, second or later recurrence, or non-endometrioid histologies (beyond carcinosarcoma/serous) were not well represented.,The 2:1 randomization results in an underpowered control arm (n=99), which may affect precision of effect estimates. __BOTTOM_LINE_CATEGORY__ not_ready_for_clinical_application __BOTTOM_LINE__ RUBY Part 2 demonstrates a statistically significant PFS benefit with niraparib added to dostarlimab maintenance after dostarlimab-based chemotherapy in primary advanced/recurrent endometrial cancer — including the pMMR/MSS population — but fails to show any overall survival advantage at 36.2 months of follow-up, with a numerically unfavorable OS HR of 1.2. Given the substantial toxicity burden (70.7% grade ≥3 TRAEs, 38.7% discontinuations), the absence of an OS benefit, and the critical comparator limitation (chemotherapy-placebo rather than dostarlimab monotherapy maintenance), the authors themselves conclude that these data do not support adding a PARP inhibitor to immunotherapy maintenance in endometrial cancer. Dostarlimab plus chemotherapy followed by dostarlimab monotherapy maintenance, which has demonstrated OS benefit in RUBY Part 1, remains the evidence-based standard of care.