Statistical analysis
The receiver operating characteristic (ROC) curves were used to identify
the potential cut-off values of preoperative serum CA19-9 in predicting
survival. The ROC curves were also used to compare the area under curves
(AUC) of the modified TNM(mTNM) staging system and the eighth edition of
the TNM staging system to show the advantage of each in predicting
survival. The OS curves were calculated using the Kaplan-Meier method
based on the length of time between the primary surgical treatment and
final follow up or death.The log-rank test was used to assess
significant differences between curves. Independent prognostic factors
were identified by the COX proportional hazard regression model which
were used to measure homogeneity and discriminatory ability.
P<0.050 (bilateral) was considered statistically significant.
The statistical analysis was performed using the statistical analysis
program package IBM SPSS 23.0 and MedCalc v.19.6.1.