Data analysis
The data collected were statistically analyzed by the statistical computer software SPSS, version 15.0. A post hoc analysis of temporal trend was performed. Descriptive statistics were calculated for all demographic and clinical variables. Continuous variables were presented as mean and standard deviation (SD), and categorical variables as frequency and percentage. The normality assumption was verified using the Shapiro-Wilk test. T-student and χ2 tests were adopted for comparisons between categorical variables. T-test and non-parametric Mann-Whitney tests were adopted for comparisons between continuous variables. Kaplan-Meier curves estimated the survival function. Statistical significance was set at levels of P < 0.05.