Occupational asbestos exposure and urinary bladder cancer: a systematic review and meta-analysis

Purpose: There is conflicting evidence on the association between asbestos exposure and bladder cancer. We performed a systematic review and meta-analysis to provide evidence on occupational asbestos exposure and the risk of mortality and incidence of bladder cancer. Methods: We searched three relevant electronic databases (Pubmed, Scopus, and Embase) from inception to October 2021. The methodological quality of included articles was evaluated using the US National Institutes of Health tool. Standardized incidence ratios (SIRs) and standardized mortality ratios (SMRs) for bladder cancer, as well as respective 95% confidence intervals (CIs), were extracted or calculated for each included cohort. Main and subgroup meta-analyses according to first year of employment, industry, sex, asbestos type, and geographic region were performed. Results: Fifty-nine publications comprising 60 cohorts were included. Bladder cancer incidence and mortality were not significantly associated with occupational asbestos exposure (pooled SIR: 1.04, 95% CI: 0.95–1.13, P = 0.000; pooled SMR: 1.06, 95% CI: 0.96–1.17, P = 0.031). Bladder cancer incidence was higher among workers employed between 1908 and 1940 (SIR: 1.15, 95% CI: 1.01–1.31). Mortality was elevated in asbestos workers cohorts (SMR: 1.12, 95% CI: 1.06–1.30) and in the subgroup analysis for women (SMR: 1.83, 95% CI: 1.22–2.75). No association was found between asbestos types and bladder cancer incidence or mortality. We observed no difference in the subgroup analysis for countries and no direct publication bias evidence. Conclusion: There is evidence that workers with occupational asbestos exposure have a bladder cancer incidence and mortality similar to the general population.