Prognostic Factors for Progression-Free Survival in Patients with Advanced Gastric Cancer Treated with First-Line Nivolumab Plus Oxaliplatin-Based Chemotherapy: Combined Clinical and Baseline CT Features

Background: Although nivolumab plus platinum-based chemotherapy has been approved as a first-line systemic treatment for advanced gastric cancer (AGC), the pretreatment imaging and clinical factors associated with disease progression remain incompletely understood. Methods: This retrospective study included 172 patients with AGC who underwent baseline CT and were treated with nivolumab plus chemotherapy. Factors associated with progression-free survival (PFS) were analyzed using univariable and multivariable Cox proportional hazards regression. The performance of the selected variables was evaluated using Harrell’s concordance index (C-index) and the time-dependent area under the curve (AUC). Results: Progression or death occurred in 79.1% of patients (136/172). The number of metastatic sites (hazard ratio [HR], 1.60; 95% confidence interval [CI], 1.28–1.99; p < 0.001), Eastern Cooperative Oncology Group (ECOG) performance status (PS) (HR, 2.02; 95% CI, 1.29–3.16; p = 0.003), macroscopic tumor morphology (HR, 1.69; 95% CI, 1.00–2.84; p = 0.049), and seeding score (HR, 1.16; 95% CI, 1.00–1.36; p = 0.049) were significant prognostic factors for PFS. Together, these four selected variables yielded a C-index of 0.69 (0.64–0.74) and a 12-month time-dependent AUC of 0.73 (0.66–0.81). Median PFS differed significantly between the low- and high-risk groups (9.6 months, 95% CI, 8.0–17.3 vs. 5.2 months, 95% CI, 4.1–6.6; p < 0.001). Conclusions: Combined clinical and CT imaging features, including the number of metastatic sites and ECOG PS, were independent prognostic factors for PFS in patients with AGC receiving first-line nivolumab plus chemotherapy.