2.5 Statistical analysis
Pairwise comparisons of the variables between groups were performed
using the Mann–Whitney U test for continuous variables and Fisher’s
exact test for categorical variables. A receiver operating
characteristic (ROC) curve was used to identify the optimal cutoff
levels that best discriminated patients in relapse. Survival functions
were estimated using the Kaplan–Meier method and were compared using
the log-rank test. The variables with P <0.20 by the
univariate analysis were entered into a multivariate model using a Cox
proportional hazards model to identify the most statistically
significant parameters associated with RFS and OS. The level for a
statistically significant difference was set at P <0.05
for all univariate tests. The SPSS 19.0 software package (SPSS Inc.,
Chicago, IL) and GraphPad Prism 5 (GraphPad Software Inc., La Jolla, CA)
were used for the data analysis.