Introduction Gotistobart (ONC-392/BNT316) is a humanized anti-CTLA-4 mAb that preserves CTLA-4 immune checkpoint activity by avoiding lysosomal degradation. The safety and clinical activity of gotistobart monotherapy in ovarian cancer was previously reported. We report safety and efficacy results of gotistobart+pembrolizumab in an ongoing randomized, open-label, multicenter phase 2 trial in patients with PROC.

Methods Patients with platinum-resistant high-grade serous OC, tubal or peritoneal cancer who previously received 1 line of platinum-based therapy and progressed between 3-6 months, or received ≥1 line and progressed within 6 months of last dose, were randomized 1:1 to receive different doses of gotistobart+pembrolizumab 200 mg, Q3W. Primary endpoints are ORR (RECIST 1.1) and safety. Secondary endpoints include PFS and OS.

Results As of May 24, 2024, 83 patients had received ≥1 dose of gotistobart+pembrolizumab with 33 and 29 patients in 1 mg/kg and 2 mg/kg gotistobart+pembrolizumab groups, respectively. At the safety and efficacy cutoff date of May 10, 2024, with a median follow-up of 2.1 months (range 0.1-9.2), grade≥3 treatment-related adverse events (TRAEs) were observed in 35.7% and 31.0% patients in 1 mg/kg or 2 mg/kg groups, respectively (table 1). No grade 5 TRAEs were observed. Common grade 3 TRAEs from combined groups were ALT increased (7.0%), AST increased (7.0%) and diarrhea (5.3%). Unconfirmed ORR was 31.8% (7/22; 95% CI 13.9-54.9) and 36.4% (8/22; 95% CI 17.2-59.3) in 1 mg/kg and 2 mg/kg groups, respectively (table 1).

Conclusion/Implications Early results show encouraging safety and clinical activity in PROC patients receiving gotistobart+pembrolizumab.

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Abstract LB010/#1590 Figure 1

Waterfall plot of best change in tumor burden and best overall response*