Statistical analysis
The independent data monitoring committee performed an interim analysis every 6 months. We used the Haybittle-Peto boundary to determine the upper and lower stopping boundaries for the primary outcome, with no adjustment in the final analysis.The survival outcomes were analysed without adjustment in the intention-to-treat population, which included all the patients who were randomized. All included patients were confirmed to have received the assigned intervention. Trial data were summarized by the calculation of means and standard deviations for normally distributed variables, median and interquartile ranges for nonnormally distributed variables, and frequency and percentage for categorical variables. The magnitude of the difference between two percentages was demonstrated by the risk difference with 95% confidence intervals. All statistical tests were two-sided. A p value less than 0.05 was considered statistically significant. All analyses were performed using STATA software version 14.0 (StataCorp, College Station, TX).