Development and external validation of a nomogram for predicting the effect of tumor size on survival of patients with perihilar cholangiocarcinoma

Background The effect of tumor size on account of long-term survival results in perihilar cholangiocarcinoma (PCCA) patients has remained a controversial debate. It is urgent necessary to identify the optimal cutoff value of tumor size in PCCA and integrate tumor size with other prognostic factors into a nomogram to improve the predictive accuracy of prognosis of patients with PCCA. Methods Three hundred sixty-three PCCA patients underwent surgical resection were extracted from the Surveillance, Epidemiology and End Results (SEER) database. X-tile program was used to identify the optimal cutoff value of tumor size. A nomogram including tumor size was established to predict 1-, 3- and 5-year cancer-specific survival (CSS) based on the independent risk factors chosen by Kaplan-Meier methods and multivariable cox regression models. The precision of the nomogram for predicting survival was validated internally and externally. Results PCCA patients underwent surgical resection were classified into 1-19 mm, 20-33 mm and >= 34 mm subgroups based on the optimal cutoff for tumor size in terms of CSS. And we noticed that more larger tumor size group had worse tumor grade, advanced T stage, more positive regional lymph nodes and more frequent vascular invasion. 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 the larger tumor size of PCCA was, the worse survival would be. The proposed nomogram, which outperforms the conventional TNM staging system, showed relatively good performance and could be considered as convenient individualized predictive tool for prognosis of PCCA patients.