First-line (1L) anti-PD-1 plus chemotherapy in HER2-negative advanced gastric cancer: Real-world evidence from a single Korean center.

83 Background: The implementation of immune checkpoint inhibitor combinations as first-line (1L) treatment has shown promising outcomes and is now the standard of care for HER2-negative advanced gastric cancer. However, real-world evidence supporting this approach as 1L treatment remains limited. Here, we present an analysis of real-world outcomes, comparing 1L anti-PD-1 combined with doublet chemotherapy to the previous standard chemotherapy. Methods: Patient from January 2005 to August 2023 were retrospectively reviewed. The study defined the molecular epidemiology cohort (M cohort) as patients with results for HER2, Epstein-Barr virus (EBV), mismatch repair (MMR), or PD-L1. HER2-negative patients who received palliative first-line chemotherapy doublet regimens with or without PD-1 inhibitor were included. Survival analysis included progression-free survival (PFS) and overall survival (OS), as well as subgroup analyses for molecular subtypes. Results: Total 3,028 were enrolled in the M cohort. The incidence rates of HER2-positive, EBV-positive, and deficient Mismatch Repair (dMMR) were 20.0% (606/3028), 3.8% (93/2432), and 4.7% (126/2660), respectively. PD-L1 testing was conducted on 1,394 patients, with 54.3% (1634/3028) having a CPS (Combined Positive Score) of ≥10, and 47.6% (664/1394) having a CPS of ≥1. Among these patients 1,527 had received chemotherapy doublet, and 153 had received chemotherapy doublet with PD-1 inhibitor as their 1L treatment. During a median follow-up of 56.5 months (95% CI,49.9-66.2), patients who had received PD-1 inhibitor combination therapy showed improved PFS (7.1 vs. 6.1 months; Hazard Ratio [HR], 0.77; 95% Confidence Interval [CI], 0.64–0.93) and OS (18.1 vs. 14.6 months; HR 0.80; 95% CI, 0.63–1.01) compared to those without it. The benefits in PFS from PD-1 inhibitor combination therapy were particularly notable in patients with deficient MMR status (HR, 0.22 vs. 0.80 in those without PD-1 inhibitor combination; p for interaction <0.05) and in patients with signet ring cell carcinoma histology (HR, 0.58 vs. 0.92 in those without PD-1 inhibitor combination; p for interaction <0.05). Conclusions: We observed real-world efficacy of the combination of PD-1 inhibitor and chemotherapy doublet as 1L treatment for HER2-negative advanced gastric cancer, consistent with previous clinical trials. [Table: see text]