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Comparative effectiveness of nivolumab (NIVO) relative to standard of care (SOC) for advanced/metastatic (adv/met) gastric or gastroesophageal junction cancer (GC/GEJC): A simulated treatment comparison (STC).

128 Background: The prognosis of adv/met GC/GEJC among patients receiving third and later lines (L) of therapy is poor, and effective treatment options are limited. The study objective was to estimate the relative effect of NIVO versus SOC for overall survival (OS), in the US among adv/met GC/GEJC patients who received ≥ 3L therapy. Methods: A STC was performed using individual patient data from the single-arm CheckMate 032 (CM032) trial, and the Flatiron Health (FH) database. Eligible patients had adv/met GC/GEJC and received NIVO (CM032) or SOC (FH) as ≥ 3L therapy; all patients met CM032 eligibility criteria. A regression model of OS was fit to CM032 data using prognostic factors and treatment effect modifiers identified through a systematic literature review. The regression model was used to predict OS for NIVO, using Flatiron patient characteristics as covariates, and to estimate the expected outcome if NIVO had been available in the Flatiron population. The observed and predicted OS for NIVO was compared against the observed OS for SOC to generate naïve and adjusted hazard ratio comparisons of NIVO vs SOC. Results: In total, 42 and 43 patients were included from CM032 and Flatiron, respectively. In the Cox model, 19 prognostic factors were considered and the final model adjusted for 6, based on data availability across the two sources: ECOG, alkaline phosphatase (ALP) and hemoglobin, sex, prior surgery, and tumor location. Median OS was 8.97 months in the NIVO group and 5.61 months in the SOC group. The STC adjustment yielded a hazard ratio of 0.66 (95% CI: 0.41 to 1.06) for NIVO vs SOC compared to the naïve estimate of 0.64 (0.40 to 1.03). Sensitivity analyses confirm this result. Conclusions: In the absence of head-to-head data, this study suggests that NIVO may confer a benefit in terms of OS versus SOC for patients with GC/GEJC in ≥ 3L therapy in the US setting. Despite the inherent limitations of using non-randomized comparisons of clinical trial data and real-world evidence, these findings provide insight into the potential benefit of novel agents such as NIVO.