Sex differences in the risk of bladder cancer among kidney transplant recipients and patients with kidney failure receiving hemodialysis: a nationwide cohort study.

Introduction: Although both patients with kidney failure (KF) receiving hemodialysis (HD) and kidney transplant (KT) recipients (KTRs) have a high risk of bladder cancer, how this risk changes in the transition from dialysis to KT is unknown. In this study, we aimed to investigate the risk of bladder cancer in KTRs and patients on HD.

Methods: This was a nationwide longitudinal cohort study of 66,547 participants from the National Health Insurance Service cohort who started HD for KF or received KT from 2002 to 2020. The primary outcome was the diagnosis of bladder cancer, which was defined as the composite of diagnostic codes and either hospitalization or ≥2 outpatient visits for bladder cancer.

Results: During mean follow-ups of 4.2 and 7.9 years in the HD and KT groups, respectively, the incidence rates of bladder cancer were 1.1/1,000 and 0.3/1,000 person-years, respectively. In the time-dependent multivariable Cox models, compared to patients on HD, the adjusted hazard ratio (aHR) for bladder cancer among KTRs was 0.36 (95% confidence interval [CI], 0.21-0.60; p<0.001). Among men, this aHR was 0.29 (95% CI, 0.15-0.55; p<0.001); however, no statistically significant association between the kidney replacement therapy modality and the risk of bladder cancer was observed among women. Landmark analysis performed to avoid immortal time bias by redefining time zero as a specific landmark time (2 and 5 years after HD initiation or KT) revealed similar results.

Conclusion: The risk of bladder cancer was significantly lower among KTRs than that among patients receiving HD, particularly among men.