Envafolimab plus chemotherapy in advanced gastric or gastroesophageal junction (G/GEJ) cancer.

e16585 Background: Envafolimab is a novel fusion protein of humanized anti-PD-L1 single domain antibody and human IgG1 Fc, formulated for subcutaneously (SC) injection. This study examined the feasibility of combining envafolimab with chemotherapy in advanced G/GEJ cancer. Methods: This study was a single arm, phase Ⅱ trial in adult subjects with previously untreated advanced G/GEJ cancer. Subjects received 8 cycles (2 weeks each) of envafolimab plus FOLFOX regimen followed by envafolimab and 5-FU until progression or unacceptable toxicity. Envafolimab was administrated SC at 5 mg/kg on day 1 of each cycle; FOLFOX consisted of 80 mg/m 2 oxaliplatin, 400 mg/m 2 5-FU and 400 mg/m 2 leucovorin intravenous infusion on day 1, 2400 mg/m 2 5-FU administered with a 48-hour continuous infusion on day 1 and 2. Tumor was assessed every 6 weeks per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1). Primary endpoints were safety and tolerability. Toxicity was graded using CTCAE v5.0. Secondary endpoints included objective response rate (ORR), duration of response (DoR). and progression free survival (PFS). Results: A total of 15 subjects were treated and evaluable for response. ECOG performance status was 1 in 80% of subjects. Majority had gastric cancer (86.7%). At the data cutoff, the minimum follow-up was 6 months. The treatment emergent adverse event (TEAE) occurrence was 100% (all grades) and 73.3% (grades 3-4). The most frequent grade 3-4 TEAE included neutrophil count decreased 46.7%, anemia 20.0%, and platelet disorder 20% (3/15). Confirmed ORR was 60% (unconfirmed ORR: 73.3%). Median DOR was not reached. Median PFS was 6.8 months. Conclusions: Envafolimab plus FOLFOX demonstrated a manageable safety profile with promising clinical efficacy as a first line therapy for advanced G/GEJ cancer. Clinical trial information: CTR20181124 .