Benzene exposure at workplace and risk of colorectal cancer in four Nordic countries.

OBJECTIVE: The aim of this case-control study was to assess the effect of occupational benzene exposure on the risk of colorectal cancer, including its subtypes.

METHODS: The study included 181,709 colon cancer and 109,227 rectal cancer cases diagnosed between 1961 and 2005 in Finland, Iceland, Norway and Sweden. Cases were identified from the Nordic Occupational Cancer Study (NOCCA) cohort. Five controls per case were selected from the same cohort, matched for country, birth year, and sex. Occupational benzene exposure for each study participant was estimated by linking their job titles to country specific job-exposure matrices. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by using conditional logistic regression models. The results were adjusted for physical strain at work, formaldehyde, ionizing radiation and wood dust.

RESULTS: Increased risk was observed for all colorectal cancer (OR = 1.12, 95% CI 1.05-1.18) for the high decile of cumulative benzene exposure, indicating a statistically significant dose-response relationship. This excess risk was mainly seen in ascending colon (OR = 1.27, 95% CI 1.13-1.43), and transversal colon (OR = 1.21, 95% CI 1.01-1.41). The ORs in the highest exposure category were markedly higher in women than in men in all subsites of colon and rectum.

CONCLUSION: This study showed an association between workplace benzene exposure and colorectal cancer. The risk was restricted to ascending and transversal colon, and was the strongest among women.