Poster Presentation 2025 Joint Meeting of the COSA ASM and IPOS Congress

Time to subsequent therapy in patients with primary advanced or recurrent endometrial cancer (pA/rEC) receiving dostarlimab plus carboplatin-paclitaxel (DOST+CP) compared with patients receiving placebo plus CP (PBO+CP) in the ENGOT-EN6-NSGO/GOG-3031/RUBY trial (126377)

Cara Mathews 1 , Nicoline Raaschou-Jensen 2 3 , Carolyn McCourt 4 , Filip Fruhauf 5 6 , Lucy Gilbert 7 , Evelyn L Fleming 8 , Giorgio Valabrega 9 10 , Noelle G Cloven 11 , Dominik Denschlag 12 , Iwona Podzielinski 13 , Ingrid A Boere 14 , Joseph Buscema 15 , Kathryn P Pennington 16 , Nicole S Nevadunsky 17 , Eirwen M Miller 18 , Mark S Shahin 19 , Daniel Gregory 20 , Grace Antony 21 , Laura Austin 22 , Matthew A Powell 23 , Mansoor Raza Mirza 24 25
  1. Legorreta Cancer Center, Alpert Medical School of Brown University, Providence, RI, USA
  2. NSGO, Copenhagen, Denmark
  3. Herlev Hospital, Herlev, Denmark
  4. Division of Gynecology Oncology, Department of Obstetrics and Gynecology, Washington University School of Medicine, Washington University in St Louis, St Louis, MO, USA
  5. Department of Obstetrics, Gynecology and Neonatology First Faculty of Medicine, Prague, Czech Republic
  6. Charles University and General University Hospital in Prague, Prague, Czech Republic
  7. Division of Gynecologic Oncology, Research Institute, McGill University Health Centre, Gerald Bronfman Department of Oncology, McGill University, Montreal, Canada
  8. Division of Gynecologic Oncology, Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center, Lebanon, NH, USA
  9. Department of Oncology, University of Turin, Turin, Italy
  10. Medical Oncology, Ordine Mauriziano Hospital, Turin, Italy
  11. Texas Oncology, Fort Worth, TX, USA
  12. Head of the Department OB/GYN, Director of Breast- and Gynecologic Oncology Cancer Center, Hochtaunus-kliniken, Bad Homburg, Germany
  13. Department of Gynecologic Oncology, Parkview Health, Fort Wayne, IN, USA
  14. Department of Medical Oncology, Erasmus MC Cancer Centre, Rotterdam, The Netherlands
  15. Gynecologic Oncology, Arizona Oncology, Tucson, AZ, USA
  16. Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, Fred Hutchinson Cancer Center, University of Washington School of Medicine, Seattle, WA, USA
  17. Department of Obstetrics, Gynecology, and Women’s Health, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY, USA
  18. Division of Gynecologic Oncology, Western Pennsylvania Hospital, Allegheny Health Network, Pittsburgh, PA, USA
  19. Hanjani Institute for Gynecologic Oncology, Abington Hospital–Jefferson Health, Asplundh Cancer Pavilion, Sidney Kimmel Medical College of Thomas Jefferson University, Willow Grove, PA, USA
  20. GSK, Melbourne, VIC, Australia
  21. GSK, London, UK
  22. GSK, Upper Providence, PA, USA
  23. Washington University School of Medicine, Siteman Cancer Center, St Louis, MO, USA
  24. Department of Oncology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
  25. Nordic Society of Gynaecologic Oncology-Clinical Trial Unit, Copenhagen, Denmark

Background/rationale: In Part 1 of the phase 3 RUBY trial (NCT03981796; funding: GSK), DOST+CP significantly improved progression-free and overall survival in patients with pA/rEC. Time to first subsequent therapy (TFST) and second subsequent therapy (TSST) can offer insights on the regimen’s clinical benefit and its impact beyond first progression.

Methods: Patients were randomized 1:1 to receive DOST+CP or PBO+CP Q3W (6 cycles) followed by DOST or PBO monotherapy Q6W for ≤3 years (target accrual: 470 patients). Post-hoc second interim TFST and TSST analyses were performed in the overall, mismatch repair deficient/microsatellite instability-high (dMMR/MSI-H), and mismatch repair proficient/microsatellite stable (MMRp/MSS) populations (data cutoff: 22/09/2023). TFST and TSST: time from randomization to the date of the first dose of first or second subsequent anticancer therapy after study drug, respectively, or death by any cause, whichever occurred first.

Results: Of 494 randomized patients (DOST+CP: n=245; PBO+CP: n=249), 118 were dMMR/MSI-H (n=53; n=65) and 376 were MMRp/MSS (n=192; n=184). Median TFST and TSST were longer with DOST+CP than PBO+CP in the overall population (15.3 vs 10.2 months, hazard ratio [HR] 0.63, 95% CI 0.51-0.78 and 31.3 vs 19.9 months, HR 0.67, 95% CI 0.53-0.85, respectively), dMMR/MSI-H population (not reached [NR] vs 10.5 months, HR 0.34, 95% CI 0.20-0.57 and NR vs 24.0 months, HR 0.41, 95% CI 0.23-0.74, respectively) and MMRp/MSS population (12.7 vs 10.2 months, HR 0.73, 95% CI 0.58-0.92 and 26.8 vs 18.7 months, HR 0.73, 95% CI 0.57-0.94, respectively).

Conclusion: Prolonged TFST and sustained benefits through TSST with DOST+CP vs PBO+CP were reported across the overall, dMMR/MSI-H, and MMRp/MSS populations in the RUBY trial, supporting the frontline use of DOST+CP in all patients with pA/rEC.

© 2025 American Society of Clinical Oncology, Inc. Reused with permission. This abstract was accepted and presented at the 2025 ASCO Annual Meeting. All rights reserved.