Occupational Benzene Exposure Associated With Colorectal Cancer

Benzene exposure due to occupation may be associated with colorectal cancer according to a new review published in Environmental Research.¹ Future studies into individual-level exposure will likely be needed to corroborate the findings.

Colorectal cancer is the third most common type of cancer in the world and second leading cause of cancer death. Lack of physical activity, obesity, diet, and tobacco smoking are among the primary risk factors of colorectal cancer, but environmental factors, such as exposure to benzene, have been identified as potential factors in colorectal cancer.²

Benzene is known for its harmful effects on the health of those who come in contact with it, but the association between colorectal cancer and benzene has less literature corroborating its existence. This review aimed to summarize current literature to establish what the association between benzene and colorectal cancer is.

Benzene | Image credit: sulit.photos - stock.adobe.com

The researchers used Pubmed, Embase (through Ovid), and Scopus to conduct the systematic review. The search was completed in December 2022 and updated in April of 2024. All titles and abstracts were screened by the researchers and were determined for inclusion. Studies included in the review had to be peer-reviewed reports with original data that were written in English, Italian, Spanish, German, or French; were investigating mortality or incidence of certain cancers; reported a measure of association; were cohort studies or nested case-control studies; and were focused on workers in industries where they would be exposed to benzene.

Studies were excluded if they were community-based cohorts or nested case-control studies; cross-sectional and descriptive studies; systematic reviews; studies focused on non-occupational exposure; studies where the main exposure at their job was not benzene; meta-analyses; and studies that only focused on leukemia, lymphoma, or myeloma. Data were extracted from all studies, and relative risk (RR) was calculated for the association between benzene exposure at work and colorectal cancer.

There were 28 studies included in the review on colorectal cancer, 20 of which were included in a meta-analysis specifically about colon cancer, and 17 on rectal cancer. Most of the studies came from Europe (46.4%) and North America (35.7%); the studies also mostly included only male participants (57.1%).

A positive association between occupational benzene exposure and colorectal cancer was found in the meta-analysis (RR, 1.10; 95% CI, 1.06-1.14). Colorectal cancer incidence (RR, 1.10; 95% CI, 1.06-1.15) and mortality (RR, 1.04; 95% CI, 0.97-1.11) showed associations with occupational benzene exposure when outcomes were analyzed separately.

Rectal cancer had no clear association to occupational benzene exposure when analyzed in a meta-analysis of incidence and mortality combined (RR, 1.04; 95% CI, 0.96-1.13) as well as incidence (RR, 1.04; 95% CI, 0.94-1.14) and mortality (RR, 1.05; 95% CI, 0.92-1.19) separately.

Colon cancer, however, had a positive association for incidence and mortality combined (RR, 1.13; 95% CI, 1.07-1.19) to benzene exposure. This association remained the same when the mortality (RR, 1.08; 95% CI, 0.99-1.19) and colon cancer incidence (RR, 1.12; 95% CI, 1.01-1.24) were separated.

"The findings of our study suggest that occupational benzene exposure is associated with colorectal cancer, mainly due to a positive association with incidence," the authors explained. "Results were similar for colon cancer, whose incidence showed an association with benzene. For all considered outcomes and colorectal cancer subtypes, subgroup and sensitivity analyses were substantially in line with these findings."

There were some limitations to the study. There was a lack of information about confounders that could affect the association and a sensitivity analysis could not be conducted. Co-exposure with other carcinogens were not considered in most of the studies included. Most studies included are those based on assessing the jobs’ association with colorectal cancer rather than assessing their exposure individually and could lead to exposure misclassification. Different aspects of exposure were not assessed for their relation to colorectal cancer, including their dose of exposure and workload. The association between different colon segments could not be assessed due to lack of data.

Occupations that include exposure to benzene could be a cause of colorectal cancer in this population. Further studies should focus on confounders that could potentially affect this association.

References

1. Sassano M, Seyyedsalehi MS, Boffetta P. Occupational benzene exposure and colorectal cancer: a systematic review and meta-analysis. Environ Res. Published online May 21, 2024. doi:10.1016/j.envres.2024.119213
2. Talibov M, Sormunen J, Hansen J, et al. Benzene exposure at workplace and risk of colorectal cancer in four Nordic countries. Cancer Epidemiol. 2018;55:156-161. Doi:10.1016/j.canep.2018.06.011