Cancer risk in asphalt workers and roofers: review and meta-analysis of epidemiologic studies

Twenty epidemiologic studies have described cancer risk in asphalt workers and roofers in various countries. A current concern for these workers is the potential carcinogenicity posed by inhalation of bitumen fumes or dermal exposure to bitumens. Bitumens are chemically different from many carcinogenic coal-tar based materials. Both have been employed in road paving and waterproofing. We examined and combined the results of the epidemiologic studies conducted on asphalt workers and roofers. We examined the cancer risk separately in three broad job categories: 1) roofers (exposed to bitumen fumes and previously often to coal-tar fumes); 2) highway maintenance workers (HMWs) and road pavers (exposed to bitumen fumes as well as possibly coal-tar fumes previously); and 3) miscellaneous and unspecified bitumen/asphalt workers. In roofers, an increased risk was suggested for cancers of the lung (aggregated relative risk 1.8, 95% confidence interval 1.5-2.1), stomach (1.7, 1.1-2.5), nonmelanoma skin (4.0, 0.8-12), and leukemia (1.7, 0.9-2.9). Some of the excesses may be attributable to polycyclic aromatic hydrocarbons (PAH) from coal-tar products. The aggregated relative risks in road pavers and HMWs were consistently lower than in roofers for cancers of the lung (0.9, 0.8-1.0), stomach (1.1, 0.8-1.5), bladder (1.2, 0.7-1.8), skin (2.2, 1.2-3.7), and leukemias (1.3, 0.9-1.8). Their risk of skin cancer was significantly increased, based on one study. Miscellaneous and unspecified workers had a significant excess (1.5, 1.2-1.8) of lung cancer. The data were poorly focused to address the carcinogenicity of bitumen fumes, as contrasted with tar-derived exposures. For the prospect of shedding more light on the bitumen-cancer controversy, the feasibility of a powerful multicenter cohort is currently being studied by the International Agency for Research on Cancer (IARC).