Alzheimer disease (AD) is the primary cause of chronic progressive dementia worldwide, accounting for about 60-80% of all cases of dementia. It is a progressive neurodegenerative disorder affecting 50 million people around the world, and the number will continue to increase in future with the aging of the population. The public health burden arising from AD is expected to increase dramatically in the coming decades according to demographic trends.

Recently, accumulating experiments showed that BCG treatment could prevent, delay, and even reverse cognitive decline in various animal models for AD. To date, several retrospective observational cohort studies have reported the influence of BCG use or not on AD incidence in bladder cancer patients, but with controversial results. So far, the efficacy of BCG on the risk of AD in bladder cancer patients has not been systematically evaluated yet. Hence, our current exploratory meta-analysis aimed at investigating the efficacy of BCG in reducing AD risk among bladder cancer patients, though the relatively limited number of high-quality studies are available.