Table 4.45 presents the findings considered most relevant by the committee in drawing its conclusion on the possibility of an association between exposure to combustion products and multiple myeloma, presented in reverse chronologic order within type of study design.
On the basis of self-reported exposure to diesel-engine exhaust, Boffetta et al. (1988) defined a cohort of men who were 40–79 years old at the time of enrollment in the ACS prospective cohort study. Persons who had an extant cancer diagnosis at the time of enrollment were not excluded. After 2 years of followup, comparison of multiple-myeloma mortality in the diesel-exhaust-exposed cohort with that in the complementary nonexposed cohort yielded a mildly increased estimated risk (RR 1.21). After 4 years of followup on the ACS cohort, Boffetta et al. (1989) conducted a more conventionally designed nested case-control study that considered only people who had been cancer-free at the time of enrollment. Exposure to combustion products was addressed in self-reports and the even less specific surrogate of main occupation. The risks posed by the three categories of combustion-product-related agents (coal tar, pitch, or asphalt; diesel exhaust; and gasoline exhaust) showed no consistent pattern. Fully adjusted risks of multiple myeloma were increased but imprecise in truck drivers (OR 2.8, 95% CI 0.5–16.1) but more emphatically increased in railroad workers (OR 7.1, 95% CI 1.2–43.6), although both estimates were based on only three exposed cases.
Wong et al. (1999) matched each of 11 multiple-myeloma deaths observed among 9,026 land-based petroleum-distribution workers with up to five controls on sex, year of birth, and company. None of the occupational groups (mechanics, drivers, and loaders) that might be expected to have job-related exposure to diesel exhaust had an increased rate of multiple myeloma. None of the available surrogates of dose (cumulative and peak HC exposures, duration of employment or of exposure, and year of first exposure) was found to be associated with multiple myeloma in logistic regressions.
Lee et al. (2003) contrasted the occupational exposure of 446 people who had primary incident multiple-myeloma cases in 1971–1999 in a cohort of 365,424 male Swedish construction workers with that of the remainder of the cohort. A JEM was developed on the basis of exposure monitoring conducted from 1971 to 1976 and used to determine each worker’s exposure to several substances, including diesel exhaust and asphalt. There was no association between asphalt exposure and multiple myeloma. With adjustment for age, BMI, and the other occupational exposures, the risk associated with diesel exhaust exposure was slightly increased (OR 1.3, 95% CI 1.00–1.77), but a dose-response relationship was not apparent over the three exposure levels used.
In the set of 698 multiple-myeloma cases gathered from the SEER system in 1977–1981, working as a vehicle mechanic, the occupation most closely associated with combustion-product exposure, showed no association with multiple myeloma, with or without the proxy cases included (Demers et al. 1993). Self-reported exposures to diesel, jet-fuel, or automobile exhaust; coal fumes; and smoke were grouped as “carbon monoxide” (Morris et al. 1986). After adjustment for age, sex, race, and study site, the adjusted OR for all cases was 1.8 (95% CI 1.0–3.2); the reliability of this finding was increased by the fact that the result was a bit stronger