Associations between occupational exposure to chromium (VI) and cancers of the oral cavity, small intestine, pancreas, prostate and urinary bladder: systematic review and meta-analyses

Hexavalent chromium (Cr(VI)) is a human carcinogen. It is unclear whether Cr(VI) can cause cancer of the small intestine, oral cavity, pancreas, prostate and urinary bladder. We performed a systematic review and meta-analyses of epidemiological studies on occupational exposure to Cr(VI) and incidence and mortality of these cancer sites.A comprehensive review of human studies on Cr(VI) and cancer was performed in Embase and Scopus. 131 potentially relevant epidemiological studies were identified. Study quality was assessed using the Newcastle-Ottawa Scale. 29 publications including 81 observations for meta-analyses were based on cohort or case-control studies with exposure assessment of sufficient quality. Site-specific random-effects meta-analyses were done separately for incidence and mortality. Sensitivity analyses focused on the studies with the highest quality scores.No indications for an association between Cr(VI) exposure and oral or small intestine cancer were found. Incidence of pancreatic cancer was not associated with Cr(VI) exposure (meta-relative risk (RR) 1.04; 95% CI 0.85 to 1.28) while for specific mortality RR was 1.41 (95% CI 0.96 to 2.08) with moderate heterogeneity (I 2=41%) and an asymmetric funnel plot (Egger's test; p=0.002). For incidence of prostate cancer meta RR was 1.16 (95% CI 0.99 to 1.37) while the RR for mortality was 1.03 (95% CI 0.84 to 1.25). For bladder cancer, RR was 1.04 (95% CI 0.91 to 1.20) for incidence and 1.76 (95% CI 1.20 to 2.60) for mortality.This comprehensive meta-analysis of epidemiological studies did not provide sufficient evidence that occupational Cr(VI) exposure may cause cancer of the oral cavity, small intestine, pancreas, prostate or the urinary bladder in humans.