Statistical analysis
Demographic and baseline clinical data were summarized by descriptive statistics with Excel (Microsoft, Redmond, WA, USA). Normally distributed continuous variables were presented as mean ± standard deviation (SD); non-normally distributed ones were described as median and interquartile range (IQR). Categorical variables were expressed as percentage. The Mann-Whitney U and Pearson v2 tests were used to compare continuous and categorical variables, respectively. Long-term survival odds in patients with categorical and continuous baseline risks were evaluated by the Kaplan-Meier method; the patients lost to follow-up were counted as censored. Median follow-up was determined by the reverse censoring method. P < 0.05 indicated statistical significance. Statistical analyses were performed with SPSS 21.0 for Windows (IBM Co., Armonk, NY, USA).