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.