An occupational case-control study evaluated the relationship between exposure to several types of engine exhausts and combustion products, based on an industrial-hygiene assessment of occupational history, and colon cancer (Siemiatycki et al. 1988). Exposure to diesel exhaust led to an increased risk of colon cancer (OR 1.3, 90% CI 1.1–1.6). Exposure to jet-fuel exhaust and products of wood combustion also led to increases in colon-cancer risk, but the 90% CI included the null. No increased risk was reported in association with exposure to gasoline exhaust, propane exhaust, or products of combustion of propane, natural gas, liquid fuel, coal, or coke.

Conclusion

No consistent association was observed in the studies of fuels and colon cancer reviewed by the committee. Three of the studies analyzed colon cancer and rectal cancer together (Hanis et al. 1979; Nelson et al. 1987; Ritz 1999), so the committee could not determine whether exposure to fuels may have been associated with a specific type of cancer. Although the three studies of exposure to combustion products and colon cancer reported positive associations (Gerhardsson de Verdier et al. 1992; Goldberg et al. 2001; Siemiatycki et al. 1988), the committee believes that the evidence of an association is inadequate because of the small number of studies available.

The committee concludes, from its assessment of the epidemiologic literature, that there is inadequate/insufficient evidence to determine whether an association exists between exposure to fuels or combustion products and colon cancer.

RECTAL CANCER

This review focuses on cancers of the rectum, rectosigmoid junction, and anus (ICD-9 154). Risk factors for those cancers are family history, increasing age, ethnicity, dietary habits, weight and inactivity, and tobacco and alcohol use (ACS 2004p).

In 2000, there were 14.6 new cases of rectal cancer per 100,000 people in the US (19.0 among men and 11.1 among women), and 3.0 deaths per 100,000 (4.0 among men and 2.3 among women) (Ries et al. 2004).

Fuels

Table 4.11 presents the most relevant findings reviewed by the committee in drawing its conclusion on the possibility of an association between exposure to fuels and rectal cancer.

Cohort Studies

As described in the colon-cancer section, a cohort of 10,763 workers at an Amoco Corporation oil refinery employed in 1970–1980 was retrospectively studied (Nelson et al. 1985, 1987). No specific digestive-tract cancer sites were included in analysis. Increased SMRs were found for jobs associated with light aromatic hydrocarbon exposure and occasional exposure to heavy oils. For the reasons described above, it is likely that most of the digestive-tract cancers were colorectal cancers.

In a cohort of workers at Imperial Oil Limited in Canada, increased risk of colorectal cancer was assessed (Hanis et al. 1979; Lewis et al. 2000b; Schnatter et al. 1993). Colon and



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