BERKELEY, CA (UroToday Inc.) - Engine exhaust is potentially carcinogenic to humans. While evidence from animal studies suggests this, epidemiologic studies have provided limited evidence, mainly implicating only lung and bladder cancer. In Finland, a large database combines within the census both occupation and national job exposures (FINJEM). Dr. Johannes Guo and colleagues in Helsinki, Finland used this database to determine the risk of esophageal, ovarian, testicular, kidney and bladder cancers and leukemia among Finnish workers exposed to diesel or gasoline engine exhaust. They report their findings in the August 2004 issue of the International Journal of Cancer.

The study cohort comprised all economically active Finns born between 1906 and 1945 who participated in the national population census in December 1970. The population base was categorized into farmers, higher white-collar, clerical, skilled blue-collar or unskilled workers. The incident cases of the tumors studied were tabulated. The average level of exposure to diesel exhaust was assessed using the concentration of nitrogen dioxide in the air as a surrogate agent. Carbon monoxide was the indicator in assessing the exposure to gasoline engine exhaust. Diesel and gasoline engine exposures were assigned to 23 and 17 occupations respectively. Exposure to both types of engine exhaust occurred in 13 occupations.

To control for confounding non-occupational variables FINJEM contained data on lifestyle factors such as smoking, alcohol consumption and obesity. The observed and expected numbers of cases for every occupation were calculated in 5-year periods. The expected number in each stratum was obtained by multiplying the number of person-years in that occupation with the cancer incident rate of the entire Finnish population in the respective stratum. The regression analysis of the stratum-specific observed number of cases and person-years at risk was used to study exposure-response patterns.

For diesel exhaust exposure 51, 710 and 775 cases of testicular, kidney and bladder cancer respectively were observed. For exposure to gasoline engine exhaust 65, 763 and 933 cases of testicular, kidney and bladder cancer were observed respectively. Ultimately, only male cases were analyzed due to the limited number of exposed females with these diseases.

Significantly elevated standardized incidence ratios were observed for kidney cancer among male taxi drivers and male road-building machine operators and for bladder cancer among bus drivers. No exposure response relations were observed between engine exhaust and testicular cancer, esophageal cancer or leukemia. A significant increase of the relative risk was observed for kidney cancer among the men with the lowest cumulative exposure levels to diesel exhaust, but there was no increase at higher exposure levels. Also, an excess of bladder cancer was observed only at the lowest levels of exposure to gasoline engine exhaust. The observation is largely attributable to drivers, and the result is consistent with another large Nordic study.

The authors note, however, that a significant limitation of their study was the lack of information on some other known urinary carcinogens such as chemicals and aromatic amines. As another possibility, smoking increases the risk of kidney and bladder cancer and is the likely reason for excesses found among male taxi drivers, male road-building machine operators and bus drivers. Overall, the study suggested a positive exposure-response relation only between occupational exposure to diesel exhaust and ovarian cancer. An association between engine exhaust and the risk of esophageal, testicular, kidney or bladder cancers, or that of leukemia was not supported in this study.

Int J Cancer 2004; 111(2):286-92