Survival Analysis Comparing Older and Younger Patients

Categorical variables were compared using the χ² or Fisher exact test, whereas continuous variables were compared using the Mann–Whitney U test. Survival curves of the two study groups were constructed using the Kaplan–Meier method, and the survival curves were compared using the log-rank test. To identify factors independently associated with OS and DFS, univariate analysis was carried out using a Cox proportional hazards stepwise model; the significant (P < 0.05) variables were then subjected to stepwise multivariate analysis. To overcome possible selection bias, 1 : 1 PSM between the old group and young group was applied using the nearest-neighbour matching method with a caliper of 0.02 [18 (link)]. All analyses were performed using SPSS Statistics version 22.0 for Windows (IBM Corp).