According to a study published in the American Journal of Epidemiology, men with occupational exposure to asbestos appear to be more likely to develop colorectal cancer than men without such exposure.

Asbestos is the general name applied to a group of naturally occurring minerals that form fibers. These asbestos fibers have been used in a variety of applications such as textiles, cement, paper, wicks, ropes, floor and roofing tiles, water pipes, wallboard, fireproof clothing, gaskets, and brake linings. It is estimated that since the beginning of World War II, approximately 8 million people have been exposed to asbestos in the workplace.

Asbestos fibers easily break into particles. When inhaled, these dust particles can lodge in the lungs and cause damage that leads to an increased risk of lung cancer. Although the link between asbestos and lung cancer is well accepted, a possible link between asbestos and colorectal cancer is controversial. Previous studies have produced conflicting results.

In order to assess the relationship between occupational exposure to asbestos and risk of colorectal cancer, researchers evaluated data from the Beta-Carotene and Retinol Efficacy Trial (CARET). This study was originally designed to determine whether vitamin A and beta-carotene supplementation would decrease the risk of lung cancer among men and women who were at high risk for lung cancer. The study enrolled men who were occupationally exposed to asbestos and men and women who were heavy smokers. The study was stopped early when results suggested that the vitamins increased the risk of lung cancer in this high-risk population, but study participants continue to be followed.

Men were considered occupationally exposed to asbestos if they had worked at one of the following trades for at least five years: insulation, sheet metal, plumbing, plasterboard, ship fitting, ship electrical work, boiler making, or ship scaling. Participants had to have started working in these trades at least 15 years prior to their study enrollment in 1989–1993. Men were also considered occupationally exposed if they had a history of asbestos exposure in any job and chest x-ray findings consistent with asbestos-related lung disease.

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Because the CARET study participants were all heavy smokers or asbestos-exposed or both, the current analysis compared heavy smokers with asbestos exposure to heavy smokers without asbestos exposure.

The results suggest that occupational asbestos exposure increases risk of colorectal cancer:

  • Compared to heavy smokers without occupational asbestos exposure, heavy smokers with occupational asbestos exposure had a 36% increase in the risk of developing colorectal cancer.
  • Risk was particularly elevated among men with occupational asbestos exposure and evidence of asbestos-related lung disease. Among these men, risk of colorectal cancer was 54% higher than among men without occupational asbestos exposure.

The researchers conclude that men who are occupationally exposed to asbestos appear to have an increased risk of developing colorectal cancer. The researchers caution that these results may not be generalizable to women, men with lower levels of exposure to asbestos, or nonsmokers.

Reference: Aliyu OA, Cullen MR, Barnett MJ et al. Evidence for Excess Colorectal Cancer Incidence among Asbestos-Exposed Men in the Beta-Carotene and Retinol Efficacy Trial. American Journal of Epidemiology. 2005;162:868-878.

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