Bacillus Calmette-Guerin (BCG) Vaccine Impact on Dementia Risk in Bladder Cancer Patients: A Systematic Review and Meta-Analysis

Background

The BCG vaccine has been traditionally administered to prevent TB. It has been additionally used in bladder cancer patients as a therapy with success. Some observational studies found that bladder cancer patients receiving BCG may have reduced dementia risk, however, the evidence is not conclusive.

Objective

To investigate the impact of BCG vaccine on dementia risk in bladder cancer patients.

Methods

Six databases were searched from inception to January 13, 2024, for published and unpublished studies that examine the association between BCG and dementia risk in bladder cancer patients. We conducted meta-analyses using a random-effects model.

Results

Eight retrospective cohort studies were included in the systematic review and seven in the meta-analyses. Because there were studies with overlapping populations, two separate main analyses were performed reassuring the avoidance of overlap. The first analysis showed that compared to controls, BCG did not reduce dementia risk [5 studies pooled, n=88,852, HR = 0.65, 95% CI (0.40, 1.06), I² = 85%] whereas there was a marginally significant risk reduction in the second analysis [6 studies pooled, n=70,025, HR = 0.63, 95% CI (0.40, 0.97), I² = 83%]. Sensitivity analysis excluding the unpublished studies did not affect the outcome importantly. Additional meta-analysis showed that BCG did not reduce the risk of Alzheimer’s disease.

Conclusion

This meta-analysis of observational studies found that BCG administration in bladder cancer patients has likely a minimally positive impact on dementia risk if any. To better understand the effect of BCG on dementia, randomized controlled trials are needed.