Recent safety and efficacy findings from a phase 1b/2 open-label combination study of ASP-1929 photoimmunotherapy with anti-PD-1 therapy in EGFR-expressing advanced head and neck squamous cell carcinoma (HNSCC).

6083 Background: In the challenging landscape of advanced HNSCC, patients (pts) have overall low survival and high locoregional (LR) recurrence rates. While LR progression is a key contributor to morbidity and mortality, LR control remains low despite aggressive therapy including surgery, radiation, chemotherapy, and immunotherapy. ASP-1929 photoimmunotherapy (PIT) combines EGFR-targeting cetuximab, with a light-activatable dye, IRDye 700DX, and a laser light for localized drug activation. This novel approach has demonstrated rapid and selective tumor necrosis in preclinical studies, and a manageable safety profile in HNSCC early clinical trials. Phase I/II and preclinical data indicate a potential synergy in anti-tumor activity of PIT when combined with anti-PD-1 therapy. Here we present updated interim evaluation findings based on a recent data cut from this study initially presented at the 2023 American Head and Neck Society meeting. Methods: A phase 1b/2 open-label study of pts with recurrent locally advanced (rLA) and/or metastatic (m) HNSCC evaluating the safety and efficacy of ASP-1929 PIT in combination with anti-PD-1 (pembrolizumab) therapy (NCT04305795). Pts with measurable disease by modified RECIST 1.1, at least 1 lesion accessible to light illumination, combined positive score (CPS) ≥1, and who were not candidate for LR therapy could be eligible for the study. Treatment included ASP-1929 PIT (infusion day 8, target tumors illuminated 24±4 hours later) plus anti-PD-1 (days 1 objective response rate (ORR). Secondary objectives: overall survival (OS); progression-free survival (PFS); duration of response (DOR). Planned sample size: 26 HNSCC pts. Results: Of the 19 r/m HNSCC pts enrolled, 18 pts received both study therapies (PIT-evaluable). Data cut-off was August 31, 2023 (previously reported data cut-off: October 4, 2022). Efficacy results updated for the 18 PIT-evaluable pts: ORR of 33.3% (95% CI 13.3-59.0), including 4 CRs (22.2%) and 2 PRs (11.1%). Median OS not reached; 24-month OS rate estimate was 52.4% (95%CI 25.9-73.4). No change in median PFS, 2.9 months (95%CI 1.4-14.6). Median DOR was not reached at data cut-off (range 2.8+ to 18.0+ months). Safety data remained consistent with the data previously presented. Most common serious adverse reactions were dysphagia (10.5%) and tongue edema (10.5%). There were two grade 4 events: laryngeal edema (PIT-related) and tumor hemorrhage due to advanced disease, and no fatal events. Conclusions: ASP-1929 PIT in combination with anti-PD-1 therapy was generally well tolerated. Initial data demonstrate promising overall survival and response rates with this combination therapy in pts with rLA and/or m HNSCC lacking LR treatment options. Clinical trial information: NCT04305795 .