Statistical analysis
Data were analysed using SPSS (version 19.0; SPSS Inc., Chicago, IL, USA). Interval variables are presented as means ± standard deviations. Differences between groups were tested using the Mann–Whitney U test. Frequency distributions between categorical variables were compared using Pearson X 2 or Fisher’s exact tests. Survival was estimated using the Kaplan–Meier method and compared using log-rank tests. P < 0.05 (two-sided) was considered statistically significant. Cox proportional hazards models were used to estimate hazard ratios (HRs) and confidence intervals (CIs). Possible confounders were included in multivariate analyses. The independent effect of BEV use on survival and disease progression was analysed in the multivariate analysis.