Association of asbestos exposure with colorectal adenomatous polyps and cancer

Asbetos Exposure, Physical Activity and Colon Cancer: A Case-Control Study

Aims and Background

An association between colon cancer and the occupation of model or pattern maker in the car industry has been repeatedly suggested. The aim of our study was to investigate colon cancer and occupational exposures (in particular in the car industry) in an industrialized area of northern Italy.

Methods

We conducted a hospital-based case-referent study on colon cancer (n = 131; hospital controls, n = 463). All subjects were interviewed, and jobs in the car industry were investigated. Occupational exposure to asbestos and the level of physical activity were blindly assessed. All the jobs were classified according to energy expenditure (less than 8, 8-12 and more than 12 kJ/min).

Results

We found no association between colon cancer and any job in the car industry. No subject had worked as a model or pattern maker. Sedentary work was associated with colon cancer in men but not in women. An excess risk was demonstrated among males for job titles involving putative exposure to asbestos (4 cases and 3 controls; OR = 4.8, 95 % c.i. 1.05-21.5), in particular pipe fitters and boilermakers (3 cases and 1 control; OR = 10.7; 1.07-103).

Occupational exposures and colorectal cancers: A quantitative overview of epidemiological evidence

A traditional belief widespread across the biomedical community was that dietary habits and genetic predisposition were the basic factors causing colorectal cancer. In more recent times, however, a growing evidence has shown that other determinants can be very important in increasing (or reducing) incidence of this malignancy. The hypothesis that environmental and occupational risk factors are associated with colorectal cancer is gaining ground, and high risks of colorectal cancer have been reported among workers in some industrial branches. The aim of this study was to investigate the epidemiologic relationship between colorectal cancer and occupational exposures to several industrial activities, by means of a scientific literature review and meta-analysis. This work pointed out increased risks of colorectal cancer for labourers occupied in industries with a wide use of chemical compounds, such as leather (RR = 1.70, 95%CI: 1.24-2.34), basic metals (RR = 1.32, 95%CI: 1.07-1.65), plastic and rubber manufacturing (RR = 1.30, 95%CI: 0.98-1.71 and RR = 1.27, 95%CI: 0.92-1.76, respectively), besides workers in the sector of repair and installation of machinery exposed to asbestos (RR = 1.40, 95%CI: 1.07-1.84). Based on our results, the estimated crude excess risk fraction attributable to occupational exposure ranged from about 11% to about 15%. However, homogeneous pattern of association between colorectal cancer and industrial branches did not emerge from this review.

Pesticide use and colorectal cancer risk in the Agricultural Health Study

We investigated the relationship between agricultural pesticides and colorectal cancer incidence in the Agricultural Health Study. A total of 56,813 pesticide applicators with no prior history of colorectal cancer were included in this analysis. Detailed pesticide exposure and other information were obtained from self-administered questionnaires completed at the time of enrollment (1993-1997). Cancer incidence was determined through population-based cancer registries from enrollment through December 31, 2002. A total of 305 incident colorectal cancers (212 colon, 93 rectum) were diagnosed during the study period, 1993-2002. Although most of the 50 pesticides studied were not associated with colorectal cancer risk, chlorpyrifos use showed significant exposure response trend (p for trend = 0.008) for rectal cancer, rising to a 2.7-fold (95% confidence interval: 1.2-6.4) increased risk in the highest exposure category. Aldicarb was associated with a significantly increased risk of colon cancer (p for trend = 0.001), based on a small number of exposed cases, with the highest exposure category resulting in a 4.1-fold increased risk (95% confidence interval: 1.3-12.8). In contrast, dichlorophenoxyacetic acid showed a significant inverse association with colon cancer but the association was not monotonic. Our findings should be interpreted cautiously since the literature suggesting that pesticides are related to colorectal cancer is limited. Nonetheless the possibility of an association between exposure to certain pesticides and incidence of colorectal cancer among pesticide applicators deserves further evaluation.

Asbestos induces aberrant crypt foci in the colon of rats

The carcinogenicity of asbestos to the gut is controversial. The aberrant crypt focus (ACF) assay is proposed as a test for colon carcinogens. We have scored ACF in the colon of rats and mice, one month after per os gavages with suspensions of asbestos fibers. Crocidolite asbestos induced ACF in the colon of rats in two independent experiments (P = 0.02 and P < 0.01 compared to controls given water), and was ten times less effective than the carcinogen azoxymethane. Chrysotile asbestos also induced ACF in rats. Neither crocidolite nor chrysotile induced ACF in mice. The data suggest that ingested asbestos may be carcinogenic to the colon.