Development and external validation of a nomogram for predicting the effect of tumor size on cancer-specific survival of resected gallbladder cancer: a population-based study

Background The impact of tumor size on account of the long-term survival results in gallbladder cancer (GBC) patients has been controversial. It is urgent necessary to identify the optimal cut-off value of tumor size in resected GBC, and we attempted to integrate tumor size with other prognostic factors into a prognostic nomogram to predict the cancer-specific survival (CSS) of GBC patients. Methods 1639 patients with resected GBC were extracted from the Surveillance, Epidemiology and End Results (SEER) database. X-tile program was used to identify the optimal cut-off value of tumor size. A nomogram including tumor size was established to predict 1-, 3- and 5-year CSS based on the independent risk factors chosen by univariate and multivariable cox analyses. The precision of the nomogram for predicting survival was validated with Harrell's concordance index (C-index), calibration curves, and receiver operating characteristic curve (ROC) internally and externally. Results Patients with GBC were classified into 1-13 mm, 14-63 mm and 64 mm subgroup based on the optimal cut-off for tumor size in terms of CSS. The nomogram according to the independent factors was well calibrated and displayed better discrimination power than 7th tumor-node-metastasis (TNM) stage systems. Conclusions The results demonstrated that increased tumor size is closely associated with the worse CSS. Our novel nomogram, which outperforms the conventional TNM staging system, showed satisfactory accuracy and clinically practicality for predicting the outcome of resected GBC patients.