Statistical analyses

Gene methylation data were publicly available and downloaded from the UCSC Xena browser (www.xena.ucsc.edu). Methylation analysis was performed using the Infinium HumanMethylation450 BeadChip Kit (Illumina, Inc., San Diego, CA, USA). Methylation levels were calculated as previously described [39–41]. For statistical analysis, SPSS version 24 (SPSS Inc., Chicago, IL, USA) was used. Survival analyses were conducted by Kaplan-Meier and Cox proportional hazard regression analyses. P-values refer to Wald and log-rank tests, respectively. The correlation between age and methylation was tested using the Spearman’s rank correlation coefficient (ρ). For comparison between groups, Mann-Whitney U test, one-way analysis of variance (one-way ANOVA), and Fisher’s exact test were employed. P-values lower than 0.05 were considered significant.