NRG-GI007: Secondary endpoints of safety assessment and clinical complete response (cCR) of chemoradiation with endoscopically injected oncolytic virus OBP-301 in medically inoperable esophageal cancer.

435 Background: Definitive chemoradiation (CRT) is a standard-of-care for patients (Pts) with medically inoperable esophageal cancer (EC). The NRG/RTOG 0436 study of cisplatin/paclitaxel and RT (+/- cetuximab) as definitive therapy showed that 58% of control arm Pts have locally persistent disease. OBP-301 is a conditionally-restricted, replication-competent adenovirus derived from human adenovirus type 5 that adds a human Telomerase Reverse Transcriptase gene promoter, replicating only in tumor cells to cause lysis.It may cause immunogenic cell death, enhance RT increasing radiosensitization by blocking DNA repair and improve local control. Methods: In NRG-GI007, a phase 1 study (NCT04391049), OBP-301 was added to weekly carboplatin/paclitaxel and RT (50.4 Gy/28 fxs) for medically inoperable EC Pts with pathologically proven adenocarcinoma or squamous cell carcinoma (SCC) of the esophagus or Siewert Type I/II gastroesophageal junction. Pts receive 1-2mL of intratumoral OBP-301 1×10 12 virus particles/ml via endoscopy 3 days prior to and then at days 12 and 26 of CRT. The primary endpoint was protocol-defined dose-limiting toxicity, already reported. Secondary endpoints reported here are treatment-related (definitely or probably related to any protocol treatment) AEs - all and grade 4+ non-hematologic, and cCR in the primary tumor, defined as negative EGD/biopsy 6-8 weeks post-CRT. Per the protocol design, no statistical testing is done for these endpoints. Results: Initially, 6 evaluable (eligible and started protocol treatment) Pts were enrolled from June 2020 to April 2023. As initial dose level was deemed safe, an additional 9 Pts were enrolled from August 2023 to July 2024, totaling 15 evaluable Pts for secondary endpoints. Median age was 74 years, 9 Pts (60%) with ECOG PS 1. 11 Pts (73%) had adenocarcinoma and 4 had SCC; 11 Pts had N+ disease. 14 Pts (93%) received all planned OBP-301 injections and received 50.4 Gy RT. The most common treatment-related grade 3/4 AEs were decreased neutrophil (6 Pts; 40%) and lymphocyte counts (5 Pts; 33%), expected with CRT. No grade ≥3 OBP-301-related non-hematologic AEs were reported. 2 Pts died prior to restaging neitherdefinitely or probably related to OBP-301: 1 Pt developed grade 5 respiratory failure 6 weeks after CRT (suspected RT pneumonitis), while a 2 nd Pt had an unrecognized tumor invasion of the bronchus at baseline, which worsened during week 3 of CRT, resulting in a grade 5 tracheo-esophageal fistula. 2 Pts have not yet reached time for restaging. All 11 Pts who have been restaged had a cCR, for a preliminary cCR rate of 100% (95% CI: 74.1%, 100%). Conclusions: OBP-301 + CRT is safe and the preliminary cCR rate compares favorably to the historical control from NRG/RTOG 0436. Updated safety and cCR data will be presented. A randomized study is being planned. Clinical trial information: NCT04391049 .