Statistical analysis
The above-mentioned variables were expressed as mean ± standard deviation (SDs), median (range) or number (percentage) of each group according to the distribution and type of data, which were compared by Student’s t-test, Mann-Whitney test, chi-square test or Fisher exact test, respectively. Hazard ratios (HRs) were presented with their 95% confidence intervals (CIs). Kaplan–Meier curves were used to estimate the clinic outcomes and the significant differences between two groups, which were compared with the log-rank test. The effects of risks on CIN were identifed by log-binomial regression models with forward stepwise selection. Statistical analyses were carried out using software programs (SPSS for Windows, version 22.0; IBM Corporation, Armonk, NY, USA). All tests were two-tailed and P -value of <0.05 was supposed to be statistically signifcant.