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workers, (4) railway workers, and (5) other miscellaneous occupations involving diesel exhaust
exposure. This summary will focus on the railway workers studies, which were used to derive the range
of human cancer risks associated with diesel exhaust exposure. A summary of all occupational studies
evaluating the relationship between diesel exhaust exposure and lung cancer is provided in Table 1.
Studies Of Lung Cancer Among Railway Workers
In 1959, Kaplan studied lung cancer mortality among employees of the Baltimore and Ohio Railroad.
This railroad initiated locomotive dieselization in 1935, completing this process by 1958. Workers
employed at any time between 1953 and 1958 were eligible for entry into the cohort; 154 deaths from
primary cancers of the lung or bronchus were identified. Exposure was categorized into three groups by
job type. The lung cancer SMR for the most exposed group, relative to the general population, was
0.875. The limited number of years of exposure to diesel exhaust for some members of the cohort and
the abbreviated follow-up time do not allow for sufficient latency to be informative regarding the
relationship of diesel exhaust exposure to lung cancer. In addition, no data on smoking were available.
In the Third National Cancer Survey discussed above, Williams et al. (1977) found a nonsignificant
increased risk for railroad workers among lung cancer patients, OR = 1.40, based on 12 cases (no
confidence intervals reported).
Howe et al. (1983) carried out a mortality study of 43,826 male pensioners of the Canadian National
Railroad. The cohort consisted of all male pensioners who were alive at the beginning of 1965.
Subjects were followed until 1977, by which time 933 deaths from respiratory cancer (trachea,
bronchus and lung) had been recorded. Occupations at the time of retirement were classified as
“nonexposed”, “possibly exposed” or “probably exposed”. Analysis restricted to individuals retiring
after 1950 (n = 897 cases) yielded relative risks of 1.00, 1.20 (p = 0.013), and 1.35 (p < 0.001) for
the three exposure groups, respectively (test for trend: p < 0.00l). There was little change in these
effect estimates when individuals involved in locomotive maintenance (and who therefore may have been
exposed to asbestos) were excluded from the analysis (n = 69).
This study also found coal dust to be associated with lung cancer, with a similar increasing trend with
degree of exposure. Because of a high degree of overlap between exposures to coal dust and to diesel
exhaust, the authors could not separate the effects of the two. However, since there is evidence from
animal and human studies for the carcinogenicity of diesel exhaust, but such evidence does not exist for
coal dust, the apparent effect of coal dust was more likely to have been due to confounding by diesel
exhaust, rather than vice versa. No smoking information was available for this study, although there
were increasing trends with degree of diesel exposure for mortality from emphysema (SMRs = 1.00,
1.35, and 1.44) and other smoking-related cancers combined (SMRs = 1.00, 1.08, and 1.16). The
authors suggested that since the results were based on internal comparisons little variation in smoking
would be expected among the different diesel exposure groups.
Garshick et al. (1987a) carried out a case-control study of lung cancer in U.S. railroad workers. Cases
comprised 1,256 lung cancer deaths occurring between 1981 and 1982 in the population of active or
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