Safety and efficacy of BAT8006 in combination with BAT1308 in patients with advanced endometrial cancer.

5512 Background: BAT8006 is a folate receptor α (FRα)-targeting antibody-drug conjugate (ADC), while BAT1308 is a recombinant humanized anti-PD-1 monoclonal antibody. Both agents have individually demonstrated acceptable tolerability and promising antitumor activity in solid tumors. Herein, we report a phase Ib/II trial designed to evaluate the safety and efficacy of BAT8006 in combination with BAT1308 for patients with advanced endometrial cancer. Methods: Eligible patients included those with pathologically confirmed endometrial cancer who had experienced disease recurrence or progression following at least 1 line of platinum-based chemotherapy or immunotherapy-based regimen, with no more than 3 prior lines of systemic therapy. Enrolled patients received BAT8006 (76 mg/m² or 84 mg/m²) in combination with BAT1308 (fixed dose of 300 mg) every 3 weeks until disease progression, intolerable toxicity, or other protocol-specified reasons. The primary endpoints were safety and ORR as assessed by investigators per RECIST v1.1. Results: As of December 25, 2025, a total of 45 patients with advanced endometrial cancer were enrolled in this study. The median age of the cohort was 62 years (range, 27–75 years). Among these patients, 80.0% had ECOG PS of 0, and 80.0% presented with metastatic disease at baseline. All patients had received prior platinum-based chemotherapy; additionally, 48.9% had undergone prior immunotherapy, and 15.6% had received two or more prior lines of systemic therapy. The proportion of patients with FRα positivity (defined as FRα expression ≥1%) was 62.2%. TRAEs were reported in 41 patients (91.1%). Grade ≥3 (G3) TRAEs occurred in 24 patients (53.3%), and SAEs were observed in 17 patients (37.8%). The most common TRAEs (incidence ≥20%) included leukopenia (77.8%), anemia (77.8%), neutropenia (62.2%), nausea (55.6%), thrombocytopenia (53.3%), vomiting (48.9%), lymphopenia (35.6%), pyrexia (26.7%), decreased appetite (26.7%), increased alanine aminotransferase (22.2%), and asthenia (22.2%). No cases of interstitial lung disease were reported. IrAEs occurred in 3 patients (6.7%). TRAEs resulted in dose reduction in 10 patients (22.2%) and treatment discontinuation in 2 patients (4.4%). No treatment-related deaths were recorded. Efficacy was evaluable in 34 patients. The overall ORR was 38.2% (95% CI: 22.2–56.4), and DCR was 70.6% (95% CI: 52.5–84.9). In the BAT8006 (76 mg/m²) + BAT1308 cohort, ORR was 44.4% (95% CI: 21.5–69.2) and DCR was 72.2% (95% CI: 46.5–90.3). In the BAT8006 (84 mg/m²) + BAT1308 cohort, ORR was 31.3% (95% CI: 11.0–58.7) and DCR was 68.8% (95% CI: 41.3–89.0). Conclusions: These findings suggest that BAT8006 in combination with BAT1308 may represent an effective therapeutic strategy for advanced endometrial cancer, with a manageable safety profile. Further prospective studies are warranted to validate the efficacy and safety of this combination regimen. Clinical trial information: CTR20242449.