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Studies Of Lung Cancer Among Truck Drivers
The studies that have examined the lung cancer risk to truck drivers are summarized in Table 1. These
studies have consistently reported small increases in lung cancer relative risk. However, the studies
suffer from various deficiencies, including small numbers of subjects, inadequate adjustment for
confounding, and crude exposure assessments, usually based on occupational classification. Most of
the earlier studies did not adjust for smoking. Because of evidence that truck drivers have a higher
smoking prevalence (Wynder and Higgins, 1986), individual studies that do not account for smoking
generally provide limited evidence regarding carcinogenicity. Before 1988, the two studies that took
smoking into account, Williams et al. (1977) and Hall & Wynder (1984), had ORs of 1.4 - 1.5, which
were not statistically significant. The third study that accounted for smoking (Damber and Larsson,
1985, 1987), only found significantly elevated risks in truck drivers who smoked after stratifying on age
(i.e., only for those > 70 years old at diagnosis). However, in the follow-up study, after analyzing for
duration of employment (20 or more years), elevated but nonsignificant risks were observed for all
professional drivers combined (Damber and Larsson, 1987).
By comparison, the majority of studies published since 1988 have adjusted for smoking to varying
degrees. Of the smoking-adjusted population based studies, two of four found statistically significant
increases in the relative risk for lung cancer associated with occupation as a truck driver, especially in
individuals employed for 10 or more years (Hayes et al. 1989; Swanson et al. 1993). In addition, both
studies reported some evidence of a positive trend between increased duration of employment and risk
for lung cancer. Although both found statistically significant trends (p < 0.05), the only stratum with
statistically significant relative risk estimates was that including 20 or more years’ employment as a truck
driver, with ORs of 1.5 (95% C.I. = 1.0-2.3) and 2.5 (95% C.I. = 1.1-4.4), reported by Hayes et al.
(1989) and Swanson et al. (1993), respectively.
Three of the six more recent industry-specific studies adjusted for smoking, at either the individual
(Benhamou et al. (1988) and Steenland et al. (1990)) or group level (Pfluger and Minder 1994). The
two studies of professional drivers, a portion of which included truck drivers, found significantly elevated
estimates of relative risk with smoking-adjusted ORs of 1.42 (95% C.I. = 1.07-1.89) and 1.48 (95%
C.I. = 1.30-1.68) (Benhamou et al., 1988 and Pfluger and Minder, 1994, respectively). The one
smoking-adjusted study focusing on trucking, Steenland et al. (1990), found elevated relative risk
estimates for several occupational and duration of employment categories; however, the only statistically
significant risk estimate found was for diesel truck drivers with greater than 34 years of exposure, (OR
= 1.89; 95% C.I. = 1.04-3.42).
While several population-based studies enrolled a large number of subjects overall (Williams et al.
1977; Milne et al., 1983; Hall and Wynder, 1984; Damber and Larsson, 1987; Boffetta et al. 1988),
the actual numbers of subjects occupationally exposed to diesel exhaust (considered here as truck
drivers) were small. Of the larger, general population studies (Hayes et al., 1989; Benhamou et al.,
1988; Boffetta et al., 1990; Swanson et al., 1993) and industry- or occupation-specific studies
(Ahlberg et al., 1981; Rafnsson and Gunnarsdottir, 1991; Guberan et al., 1992; Hansen et al., 1993;
Pfluger and Minder, 1994; Steenland et al., 1990) with greater numbers of truck drivers, significantly
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