Abstract CT104: Results from a phase 1 study of the anti-immunoglobulin-like transcript 4 (ILT4) monoclonal antibody MK-4830 plus pembrolizumab in patients with previously treated advanced solid tumors

Abstract Background: In the dose escalation phase of a first-in-human phase 1 study (NCT03564691), the anti-ILT4 IgG4 monoclonal antibody MK-4830 + pembrolizumab (pembro) had a manageable safety profile and demonstrated promising antitumor activity in patients (pts) with previously treated advanced solid tumors, including those with PD on immunotherapy. Here, we present safety, efficacy, and biomarker analyses for MK-4830 + pembro for the previously treated pancreatic adenocarcinoma, glioblastoma, head and neck squamous cell carcinoma (HNSCC), and gastric cancer cohorts of the expansion phase. Methods: Eligible pts were aged ≥18 y with metastatic pancreatic adenocarcinoma and 1-3 lines of prior therapy (cohort A), unresectable glioblastoma and 1 prior line of therapy (cohort B), recurrent or metastatic HNSCC that progressed on a platinum-based chemotherapy and PD- (L) 1 inhibitor (cohort C), or recurrent or metastatic gastric or gastroesophageal junction adenocarcinoma that progressed on ≥2 prior chemotherapy regimens (cohort I). Pts in cohorts A, B, and I had not previously received a PD- (L) 1 inhibitor. All pts received MK-4830 800 mg + pembro 200 mg Q3W for 35 cycles or until PD, unacceptable toxicity, or study withdrawal. Primary objectives were to evaluate safety and ORR per RECIST v1. 1 (cohorts A, C, and I) or Response Assessment in Neuro-Oncology (RANO) criteria (cohort B) by investigator assessment. Exploratory objectives included evaluating DOR and PFS per RECIST v1. 1 (cohorts A, C, and I) or RANO criteria (cohort B) by investigator assessment. Results: At data cut-off (September 27, 2023), 33 pts were enrolled and received treatment in cohort A, 20 pts in cohort B, 35 pts in cohort C, and 35 pts in cohort I. Median follow-up duration was 38. 4 mo (range, 35. 5-39. 9) in cohort A, 34. 1 mo (32. 3-36. 2) in cohort B, 37. 5 mo (33. 4-42. 1) in cohort C, and 29. 5 mo (22. 3-36. 4) in cohort I. Treatment-related adverse events (TRAEs) occurred in 15 pts (45%) in cohort A, 13 pts (65%) in cohort B, 19 pts (54%) in cohort C, and 16 pts (46%) in cohort I; grade 3 or 4 TRAEs occurred in 3 pts (9%), 0 pts, 2 pts (6%), and 4 pts (11%), respectively. No deaths due to TRAEs occurred. ORR was 6% (95% CI, 1-20) in cohort A, 5% (0-25) in cohort B, 0% (0-10) in cohort C, and 20% (8-37) in cohort I. Median DOR was 14. 3 mo (range, 14. 0-14. 7) in cohort A, 7. 4 mo (7. 4-7. 4) in cohort B, and 9. 6 mo (3. 0-27. 6+) in cohort I. Median PFS was 1. 9 mo (95% CI, 1. 6-2. 0) in cohort A, 1. 2 mo (1. 1-1. 4) in cohort B, 2. 2 mo (1. 9-4. 1) in cohort C, and 1. 4 mo (1. 3-3. 0) in cohort I. Conclusions: In pts with select previously treated advanced or metastatic solid tumors, MK-4830 + pembro had a manageable AE profile but no significant antitumor activity beyond that historically observed with pembro monotherapy. Other treatment options must be explored for these difficult-to-treat tumors. Citation Format: Lillian L. Siu, Marta Gil-Martin, Byoung Chul Cho, Ruth Perets, John Hilton, Ravit Geva, Iwona Lugowska, Martin Gutierrez, Marcelo Bonomi, Rafal Dziadziuszko, Drew Rasco, Eytan Ben-Ami, Cristina P. Rodriguez, Shabana Siddiqi, Nicole Myer, Leah Suttner, Douglas Wilson, Omobolaji O. Akala, Maria de Miguel. Results from a phase 1 study of the anti-immunoglobulin-like transcript 4 (ILT4) monoclonal antibody MK-4830 plus pembrolizumab in patients with previously treated advanced solid tumors abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr CT104.