2.5 Statistical analysis
SPSS 23.0 software was used for statistical analysis. The measurement
data are expressed as the mean ± standard deviation (±S). Differences in
quantitative parameters between groups were assessed using a t test (for
normally distributed data) or nonparametric test (for nonnormally
distributed data). Categorical variables are presented as frequencies.
OS estimated by the Kaplan-Meier method was compared using the log-rank
test. P values lower than 0.05 were considered significant.