Development and validation of a postoperative nomogram for predicting survival in gallbladder cancer patients: Insights from SEER and external cohorts.

e16314 Background: Gallbladder cancer (GBC) is a rare but highly lethal malignancy with limited treatment options. Prognostic tools for predicting long-term postoperative survival are critical for guiding personalized treatment and optimizing clinical outcomes. To address this gap, we developed and validated a postoperative nomogram to predict 1-, 3-, and 5-year overall survival (OS) in GBC patients using data from the Surveillance, Epidemiology, and End Results (SEER) database and an independent external cohort from China. Methods: We retrospectively collected data from 1,848 GBC patients who underwent surgery between 2000 and 2020 from the SEER database (17 registries). An additional external validation cohort of 108 patients from a single-center database in China was included to evaluate the model's generalizability. The primary endpoint was OS. Key variables, including age, TNM stage, chemotherapy, lymphadenectomy, and histological grade, were included based on clinical relevance and statistical significance. The SEER cohort was randomly divided into a training cohort (50%) and an internal validation cohort (50%). A multivariable Cox proportional hazards regression model was used to identify independent prognostic factors and construct the nomogram. Model performance was evaluated using the concordance index (C-index), time-dependent receiver operating characteristic (ROC) curves, calibration curves, and decision curve analysis (DCA). The nomogram was externally validated using the independent Chinese cohort. Results: The nomogram incorporating these variables demonstrated robust predictive performance, with a C-index of 0.767 in the training cohort and 0.798 in the internal validation cohort. Time-dependent ROC curves in the training cohort showed AUCs of 0.777, 0.769, and 0.800 for 1-, 3-, and 5-year OS, respectively. In the internal validation cohort, the corresponding AUCs were 0.763, 0.743, and 0.803. External validation using the independent Chinese cohort of 108 patients showed consistent results, with AUCs of 0.771, 0.835, and 0.810 for 1-, 3-, and 5-year OS, respectively. Calibration curves demonstrated excellent agreement between predicted and observed survival probabilities across all cohorts and time points. DCA confirmed significant clinical net benefits across a wide range of risk thresholds in both internal and external validations. Conclusions: This study developed and validated a nomogram for predicting 1-, 3-, and 5-year OS in GBC patients. The model, which integrates key clinicopathological variables, demonstrated robust performance in both internal and external validations, with consistent results across diverse populations. This nomogram is a reliable tool for clinicians to guide personalized postoperative management, optimize follow-up strategies, and support shared decision-making.