Chrysotile fibers in tissue adjacent to laryngeal squamous cell carcinoma in cases with a history of occupational asbestos exposure

Asbestos describes a group of naturally occurring fibrous silicate mineral compounds that have been associated with a number of respiratory maladies, including mesothelioma and lung cancer. Additionally, based primarily on epidemiologic studies, asbestos has been implicated as a risk factor for laryngeal and pharyngeal squamous cell carcinoma (SCC). The chief objective of this work was to strengthen existing evidence via empirical demonstration of persistent asbestos fibers embedded in the tissue surrounding laryngeal and pharyngeal SCC, thus providing a more definitive biological link between exposure and disease. Six human papillomavirus (HPV)-negative laryngeal (n = 4) and pharyngeal (n = 2) SCC cases with a history working in an asbestos-exposed occupation were selected from a large population-based case-control study of head and neck cancer. A laryngeal SCC case with no history of occupational asbestos exposure was included as a control. Tissue cores were obtained from adjacent non-neoplastic tissue in tumor blocks from the initial primary tumor resection, and mineral fiber analysis was performed using a scanning electron microscope equipped with an energy dispersive x-ray analyzer (EDXA). Chrysotile asbestos fiber bundles were identified in 3/6 of evaluated cases with a history of occupational asbestos exposure. All 3 cases had tumors originating in the larynx. In addition, a wollastonite fiber of unclear significance was identified one of the HPV-negative pharyngeal SCC cases. No mineral fibers were identified in the adjacent tissue of a case without occupational exposure. The presence of asbestos fibers in epithelial tissue surrounding laryngeal SCC in cases with a history of occupational asbestos exposure adds a key line of physical evidence implicating asbestos as an etiologic factor.