Poster Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2026

First-line PF-08634404 (SSGJ-707), a PD-1/VEGF bispecific antibody, + chemotherapy for advanced/recurrent endometrial cancer (EC) (146014)

Michelle Harrison 1 , Qi Zhou 2 , Xingtao Long 2 , Dong Wang 2 , Li Li 3 , Ke Wang 4 , Yumei Wu 5 , Guixiang Weng 6 , Tao Wu 7 , Yang Sun 8 , Qingshui Li 9 , Ying Yang 10 , Guiling Li 11 , Weifeng Song 12 , Matko Kalac 13 , Jing Lou 12
  1. Chris O’Brien Lifehouse, Camperdown, NSW, Australia
  2. Chongqing University Cancer Hospital, Chongqing, China
  3. Cancer Hospital Affiliated To Guangxi Medical University, Nanning, China
  4. Tianjin Medical University Cancer Institute & Hospital, Tianjin, China
  5. The Capital Medical University Affiliated Beijing Obstetrics and Gynecology Hospital, Beijing, China
  6. Linyi People's Hospital, Linyi, China
  7. The First People's Hospital of Changde, Changde, China
  8. Fujian Cancer Hospital, Fuzhou, China
  9. Shandong First Medical University Affiliated Tumor Hospital, Jinan, China
  10. Yantai Yuhuangding Hospital, Yantai, China
  11. Union Hospital Tong Ji Medical College Huazhong University Of Science and Technology, Wuhan, China
  12. 3S Bio Inc, Shenyang, China
  13. Pfizer Inc., Los Angeles, CA, USA

Aim: To report results from a phase 2 study (NCT06522828) of first-line PF‑08634404+chemotherapy in advanced/recurrent EC.

Methods: Patients with newly diagnosed stage lIl/IV or recurrent EC with low potential for cure by radiation therapy/surgery and systemic treatment-naive received PF‑08634404 5 or 10 mg/kg Q3W+chemotherpy (carboplatin AUC 5+paclitaxel 175 mg/m2) Q3W for 6 cycles, followed by PF‑08634404 maintenance treatment (up to 2 years). Primary endpoints were safety and objective response rate (ORR; RECIST 1.1).

Results: 32 patients received PF‑08634404+chemotherapy: 5 mg/kg, n=16 (14 mismatch repair proficient [pMMR], 2 MMR deficient [dMMR]); 10 mg/kg, n=16 (12 pMMR, 4 dMMR). 23 patients (72%) remained on treatment at data cutoff (Feb 1, 2026). Median duration of response (DOR) follow-up was 5.8 months (95% CI: 4.6, 7.2). Confirmed ORR in the pMMR and dMMR groups was 83% and 100% for the 5 mg/kg dose, 91% and 75% for the 10 mg/kg dose, respectively. Median progression-free survival, overall survival, and DOR were not reached for either dose. Any-grade treatment-related adverse events (TRAEs) were reported in 94% and grade ≥3 TRAEs in 69% of patients. Most common TRAEs included white blood cell count decreased (66%), neutrophil count decreased (63%), anemia (59%), and platelet count decreased (59%). No TRAEs led to death. TRAEs led to PF‑08634404 discontinuation in 2 patients (6%). Immune-related AEs occurred in 6 patients (19%): hypothyroidism (n=4), hyperthyroidism (n=3), and rash (n=2). VEGF-related AEs occurred in 17 patients (53%), most commonly blood pressure elevation (n=7) and proteinuria (n=7).

Conclusions: The promising efficacy and manageable safety profile of PF‑08634404+chemotherapy for treatment-naive advanced/recurrent EC supports further investigation of PF-08634404 in the phase 3 Symbiotic-GYN-18 study (GOG-3145/ENGOT-EN37/APGOT-EN6/LACOG 0426-EVA; NCT07578649).