Asphalt (or bitumen) is produced from the distillation of crude petroleum and used in road surfacing, roofing, and waterproofing applications. When heated during application, asphalt emits a mixture of fumes, vapors and solid particulates, including carcinogens such as polycyclic aromatic hydrocarbons (PAH), which come in direct contact with the epithelium of the upper aerodigestive tract upon inhalation. Therefore, chronic exposure among asphalt workers could potentially result in elevated risk for upper aerodigestive tract cancers. There are presently no case-control studies reporting on this relationship. There is limited evidence of an association from occupational cohort studies, although these studies offer poor control for important, potentially confounding factors, such as smoking or alcohol consumption. Thus, we have investigated the association between occupational exposure to asphalt and head and neck squamous cell carcinoma (HNSCC) in a large population-based case-control study from the greater Boston area. Occupational asphalt exposure data was available for 951 incident HNSCC cases and 1193 cancer-free control subjects, matched on age (+/- 3 years), sex, and town or neighborhood of residence. Study subjects completed a self-administered questionnaire that provided detailed data on occupational history, sociodemographics and personal characteristics, and alcohol and tobacco use. Asphalt exposure was dichotomized as exposed or never exposed based on self-reported occupation data, and also by total duration of occupational exposure to asphalt. Multivariable unconditional logistic regression was used to assess the association between asphalt exposure and HNSCC, overall and by primary tumor site. A total of 140 (14.7%) cases and 145 (12.2%) controls reported an occupational exposure to asphalt. There was a significant crude association between asphalt exposure and pharyngeal cancer (crude OR = 1.47, 95% CI: 1.09-2.00) and elevated point estimates (although non-significant) for HNSCC overall and in the larynx. However, both the magnitude and significance eroded after adjusting for age, sex, smoking, and alcohol consumption. Similarly, we observed a borderline significant dose-response between occupational duration and crude HNSCC risk, overall and for the pharynx and larynx, but, again, the magnitude and (borderline) significance eroded following adjustment for confounding factors. Since cigarettes are a substantial source of PAH exposure among smokers, we repeated the analysis restricted to never-smokers but did not observe any significant association. We found no evidence for an association between asphalt work and HNSCC risk. These observations suggest that the risk estimates for HNSCC among asphalt workers provided by occupational cohort studies may be overstated due to uncontrolled confounding.
Citation Format: Scott M. Langevin, Melissa Eliot, Michael D. McClean, Karl T. Kelsey. Head and neck squamous cell carcinoma risk among asphalt workers from the greater Boston area. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 279. doi:10.1158/1538-7445.AM2014-279