Development and Validation of a Nomogram for Predicting Lymph Node Metastasis in Incidental Gallbladder Cancer before Re-Resection.

Background: Incidental gallbladder cancer (IGBC) is often diagnosed unexpectedly during or after cholecystectomy performed for presumed benign gallbladder disease. Accurate preoperative prediction of lymph node (LN) metastasis is critical for guiding surgical re-resection strategies but remains challenging. This study aimed to develop and validate a nomogram to predict LN metastasis in IGBC patients prior to re-resection. Methods: We retrospectively analyzed 745 IGBC patients who underwent re-resection between August 2019 and October 2024. Clinical data, including demographics, comorbidities, laboratory tests, imaging findings, and histopathological features, were collected. Univariate and multivariate logistic regression analyses were performed to identify independent risk factors for LN metastasis. A nomogram was constructed based on these factors. The predictive performance of the nomogram was evaluated using receiver operating characteristic (ROC) curve analysis, calibration plots, and decision curve analysis (DCA). Results: Multivariate analysis identified tumor size > 1 cm, advanced T stage, poor differentiation, positive LN status on preoperative computed tomography imaging, and elevated serum levels of carcinoembryonic antigen and carbohydrate antigen 19-9 as independent predictors of LN metastasis. The nomogram demonstrated good discriminative ability, with an area under the ROC curve (AUC) of 0.827. Calibration plots showed good agreement between predicted probabilities and observed outcomes. DCA indicated the clinical usefulness of the nomogram. Conclusions: The nomogram based on preoperative clinical, imaging, and pathological factors provides an effective tool for predicting LN metastasis in IGBC patients before re-resection. It can assist clinicians in risk stratification and optimizing surgical strategies, potentially improving patient outcomes.