Statistical analysis
The IBM Statistical Package for Social Sciences (SPSS) Statistics v. 21 software (SPSS Inc., Chicago, IL, USA) and the easyROC web tool were used to analyze our data (8). The mean and standard deviation of descriptive data, as well as the median and minimum-maximum values, were used. Numbers and percentages are used to represent categorical variables. The Kolmogorov-Smirnov test was used to test the assumption of normality. The Mann-Whitney U test was used to compare two independent groups. Spearman correlation coefficients were used to analyze the link between quantitative variables. The univariate logistic regression test was used to estimate the factors that influence survival. Finally, the area under the ROC curve was used to estimate the performance of clinical factors in estimating survival. Statistical significance was defined as a p-value of less than 0.05.