Exposure to occupational carcinogens and risk of lung cancer: A systematic review and meta-analysis

Asbestos, silica, chromium (Cr), and nickel are among the most common and serious occupational hazards to worker's health. Although its association with lung cancer has been studied for many decades, the conclusion remains somewhat controversial. The objective was to review and summarize the epidemiological evidence on the relationship between occupational exposure and risk of lung cancer and to provide an update on this major occupational health concern. Eligible studies up to September 1, 2021 were identified. Pooled effect estimates were calculated according to the reported outcome and the study design. Cohort, cross-sectional, and case control were examined separately. Studies reporting standardized mortality ratio (SMR), standardized incidence ratio (SIR), and odds ratio (OR) were analyzed separately. Due to the significant amount of heterogeneity expected, random effects models were implemented. Subgroup analysis was performed in an attempt to explain heterogeneity. The risk of lung cancer was found to be elevated in among the included studies. The pooled SMR was 1.55 (1.44–1.68). The pooled SIR was 1.55 (1.37–1.75). The pooled OR was 1.29 (1.22–1.37). After doing subgroup analysis for different carcinogens, the pooled SMR of asbestos, silica, and Cr is 1.73 (95% confidence interval (CI) 1.53–1.96), 1.16 (95% CI 0.99–1.36), 1.76 (95% CI 1.43–2.17), respectively. For nickel, there was only one study. The risk estimates in each category were highly statistically significant (P < 0.00001). A positive exposure-response relation was found between exposure and risk of lung cancer. The results of our meta-analysis supported the carcinogenic role of silica, asbestos, Cr and nickel on the lungs, which was more pronounced at higher levels of exposure. The findings of this systematic review and meta-analysis reinforce the urgent need for robust monitoring of the exposure to occupational health risks and evaluation of the evidence supporting causal effects for each occupational risk-outcome pair.