Abstract CT044: Preliminary activity and safety of OBT076 in patients with CD205 positive solid tumors: Results from the phase 1b part B expansion cohort

Abstract Background: OBT076 is a novel ADC targeting CD205 (payload DM4). Preclinical studies demonstrated potent antitumor activity. This open label Phase 1B study (Part B) aimed to evaluate the safety and preliminary efficacy of OBT076 monotherapy in patients (pts) with CD205 positive (2+ in ≥ 50% by IHC) solid tumors. Methods: Key eligibility criteria included age ≥ 18 yrs, CD205 positivity, ECOG ≤1, and progression on/after standard treatments. Patients received OBT076 at 3.0 mg/kg intravenously Q3W until progression or toxicity. Pts who had been previously treated with anti-PD-1 directed therapy had the option to be re-challenged after progression on OBT076 with anti-PD-1 balstilimab. Primary endpoints were safety and tolerability, while secondary endpoints were overall response rate (ORR), disease control rate (DCR), and progression free survival (PFS). Results: At data cut-off of 18-December-2024, a total of 51 pts received at least one dose of OBT076 in Part B, Median age was 61 years [range: 40 -78 yrs], 56% male, 44% female, and pts had received a median of 2 [1;7] prior lines of therapy. 13 pts (15%), who progressed on prior anti-PD-1 and on OBT076 were re-challenged with balstilimab, 7 of these 13 (53%) had NSCLC. Most common tumor types enrolled included NSCLC (12 pts, 23%), ovarian cancer (9 pts, 17%) and gastric/GEJ cancer (8 pts, 15%). Safety: Most common AEs were neutropenia (41%), anemia (41%), fatigue (39%), and febrile neutropenia (39%). Three treatment-related events eye-disorders (max G2, 1 pt with G2 PT Retinal pigment epitheliopathy) were reported. Grade 3-4 AEs occurred in 94% of pts, with anemia (11%), neutropenia (39%), and febrile neutropenia (39%) being the most frequent severe adverse events. Febrile neutropenia resolved quickly in most of the cases after empiric antibiotic therapy, with the majority of cases not associated with severe infections. Dose delays were required in 13/51 (25%) of pts, dose reductions due to AE in 16/51 (31%) of pts, and 3 pts (6%) discontinued treatment due to AEs. No treatment-related deaths were reported. Efficacy: Best ORR of SD was observed in 18/51 pts (40%), 1 pt with PR in NSCLC (PFS 10.8 months), DCR overall was 37%, and in NSCLC 41%. Median PFS for pts with NSCLC was 3.9 months, 2.5 months for patients with gastric/GEJ cancer, 2.0 months for patients with ovarian cancer. No objective responses were seen in the pats who were re-challenged with balstilimab, with median time on balstilimab being 43 days [1;155]. Conclusions: OBT076 demonstrated a manageable safety profile. Neutropenia and febrile neutropenia were most frequent grade 3-4 AEs. No clinically relevant ocular events have been reported. Preliminary antitumor activity in NSCLC was comparable to the efficacy of docetaxel in this setting, with an ORR of 8.3% and median PFS of 3.9 months. These findings support further investigation of OBT076 in combination with anti-PD-1. Citation Format: Rita Saude Conde, Rutika Mehta, Cécile Vicier, Daniel Flora, Lauriane Eberst, Philip R. Debruyne, Harald Haeske, Christian Rohlff, Andrew Dickinson, Lea Chapuis, Belinda Cairns, Eric Raymond. Preliminary activity and safety of OBT076 in patients with CD205 positive solid tumors: Results from the phase 1b part B expansion cohort [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr CT044.