To further investigate if the significant association of the four biological aging genes with BCR is attributed to specific patient subgroups (that is driving significance of the association), we have performed stratified Cox proportional hazards analysis on the patient subgroups stratified by the (1) Gleason score, which is a commonly used prognostic factor for prostate cancer, and (2) chronological age, which is a known diagnostic factor for prostate cancer (Figure 3A). This evidence concerns the gene BCR and prostate cancer.