Meta-analysis of occupational exposures in the rubber manufacturing industry and risk of cancer

Abstract

Background: Occupational exposures in the rubber manufacturing industry showed an increased risk of cancer and have been classified as a group 1 carcinogen, largely from studies on workers employed before 1950s. Cancer sites considered as causally associated are bladder, lung and stomach, and leukaemia. Recent studies did not report an increased risk of cancer.

Methods: A meta-analysis was conducted on observational studies published until April 2016 on occupational exposures in the rubber manufacturing industry and risk of cancer. Case-control and cohort studies were included. Random effect models were used. Heterogeneity and publication bias were evaluated. Stratified analyses were conducted on study characteristics.

Results: The literature search identified 46 cohorts and 59 case-control studies. An increased risk was found for bladder cancer [standardised incidence ratio (SRR) = 1.36; 95% confidence interval (CI) 1.18, 1.57], leukaemia (SRR = 1.29; 95% CI 1.11, 1.52), lymphatic and haematopoietic system (SRR = 1.16; 95% CI 1.02, 1.31) and larynx cancer (SRR = 1.46; 95% CI 1.10, 1.94). For lung cancer, a borderline statistically significant increased risk was identified (SRR = 1.08; 95% CI 0.99, 1.17). No association was found for stomach cancer (SRR = 1.06; 95% CI 0.95, 1.17). In stratified analyses, risks of cancer were not increased for workers employed after 1960 for bladder cancer (SRR = 1.06; 95% CI 0.66, 1.71), lung cancer (SRR = 0.94; 95% CI 0.68, 1.29) or leukaemia (SRR = 0.92; 95% CI 0.62, 1.36).

Conclusions: Risk of bladder cancer, lung cancer, leukaemia and larynx cancer were increased among workers in rubber industry. Evidence of elevated risks was no longer seen for bladder cancer, lung cancer or leukemia among workers first employed after 1960.

Keywords: Rubber; cancer; meta-analysis; occupational exposure.