Statistical analysis
Overall survival (OS) was defined as the time from diagnosis to the date of last follow-up or death from any cause. EFS was defined as the time from diagnosis to the first event (remission failure, relapse, death, or secondary malignancy) or the last follow-up. Continuous variables were expressed as medians and ranges, while categorical variables were expressed as frequencies and percentages. The differences between different groups were analyzed using a Mann-Whitney U-test or a Chi-square test for continuous and categorical variables, respectively. OS and EFS were analyzed using the Kaplan-Meier method and a log-rank test. Cox regression analysis was performed using a multivariate analysis. Statistical analysis was performed using SPSS software (version 22.0; IBM, Armonk, NY). A P value of < 0.05 was considered statistically significant.