Colorectal Cancer and Asbestos Exposure
Exposure to asbestos has been clearly linked to the development of multiple diseases, but colorectal cancer has not definitively been included in this category. This cancer, defined as a disease of the large intestine or rectum, is considered one of the leading causes of cancer-related deaths in the United States.
Researchers are unsure of the specific cause of colon cancer, but they do attribute a culmination of risk factors that may increase the likelihood of developing it. Evidence suggests that asbestos exposure is one of these causal risk factors. However, unlike with diseases like mesothelioma, asbestos’ role is less defined.
With the addition of external risk factors like smoking, some data appears to show that a person’s chances of developing colorectal cancer when exposed to asbestos may be increased. Critics of this perspective argue that more research is needed in order to conclude a causal link between asbestos exposure and this cancer.

What the Evidence Suggests
Research studies have shown trends and patterns that suggest asbestos is a risk factor for colorectal cancer. Because this relationship has been analyzed less frequently in recent years, much of the available data is dependent on studies from prior decades.
In one study conducted between 1984 and 2004, researchers analyzed 3,897 patients who were occupationally exposed to asbestos, who were simultaneously participating in a Beta-Carotene and Retinol Efficacy Trail (CARET).
Whether the patient was a smoker was also considered in the researchers’ analysis. According to the study results, the risk of colorectal cancer was increased among men who were occupationally exposed to asbestos.
Another study of 632 insulation workers, an occupation that is known for asbestos exposure, yielded similar results. The workers who were studied entered the industry before 1943 and were analyzed until 1962. Among the group that was studied, the number of deaths reported from colon and rectum cancers were significantly higher than expected.
The authors of the study expected 5.2 deaths from colon or rectum cancers based on the population. Data revealed 17 deaths were attributed to this cancer, suggesting that asbestos exposure increases the development of coloretal cancers.
Contrasting Data
Despite scientific data that supports a link between colorectal cancer and asbestos exposure, some critics doubt the validity and clarity of the relationship. Contrasting evidence exists that suggests the link may not be present at all.
According to one report, published in International Archives of Occupational and Environmental Health in 1994, researchers studied 261 cases of colon and rectal cancer and 183 control cases in southeast Michigan. Workers from occupations with historically known asbestos exposure were analyzed.
The authors stated that the data didn’t exemplify a causal relationship. They acknowledged that asbestos exposure has been linked to colorectal cancer in other studies and reports, but found contradicting evidence within the context of their study.
Furthermore, researchers who performed an in-depth analysis of different published reports involving 20 cohorts of asbestos-exposed individuals found similarly interesting results. The study, which was published in the American Journal of Epidemiology, found that one specific type of asbestos, amphibole asbestos, may potentially be associated with colorectal cancer, but may be as a result of an improper certification of cause of death. The authors reported data that suggests serpentine asbestos is not linked to an increased risk of colorectal cancer.
Further Evidence Needed
The previously listed studies account for a portion of the research that has been presented about colorectal cancer and asbestos exposure. Despite the inclusion of thousands of relevant cases, definitive conclusions of such a link cannot be stated.
Some in the medical community believe that more research is necessary to conclude that a causal relationship exists between colorectal cancer and asbestos exposure. The need for further research does not infer that a link does not exist, but rather that researchers are unsure.

Source: http://www.asbestos.com/cancer/colorectal.php