Statistical analysis
The Kolmogorov-Smirnov test was used to verify the normal distribution of continuous variables. Variables with normal distribution were described by means and standard deviations and compared by Student’s t-test. Categorical data were presented as the number of patients and percentage of the total sample and were compared by the Fisher’s exact test. The overall survival was calculated by the Kaplan-Meier method and the log-rank test was used to compare the survival curves. A value of P <0.05 was considered as statistically significant. To identify the variables that are independently predictive of overall mortality, a subsequent stepwise multivariate analysis using Cox’s regression model was performed, including variables that had a predictive value of P-value < 0.10 in the univariate analysis.