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

Our plain-English summary of Chrysotile fibers in tissue adjacent to laryngeal squamous cell carcinoma in cases with a history of occupational asbestos exposure, by S.K. Wronkiewicz, V.L. Roggli, B.H. Hinrichs, et al (Modern Pathology, 2020).

The study

• Authors: S.K. Wronkiewicz, V.L. Roggli, B.H. Hinrichs, A. Kendler, R.A. Butler, B.C. Christensen, C.J. Marsit, H.H. Nelson, M.D. McClean, K.T. Kelsey, S.M. Langevin
• Journal: Modern Pathology
• Published: 2020;33(2):228-234
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

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. In addition, based primarily on epidemiologic studies, asbestos has been implicated as a risk factor for laryngeal and pharyngeal squamous cell carcinoma (SCC). The main 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 nonneoplastic 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 three 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 adjacent tissue of the case without occupational exposure. The presence of asbestos fibers in the 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.

In plain English

The authors examined throat tissue for asbestos fibers in six men with squamous cell carcinoma. Four had cancer of the larynx (voice box) and two of the pharynx, and all were drawn from a Boston-area case-control study. All six were HPV-negative on blood tests for antibodies to high-risk HPV and had worked in asbestos-exposed jobs, including automotive mechanic, firefighter and metal lather. One man with laryngeal cancer and no asbestos job history, a truck driver, served as a comparison. Small samples of non-cancerous tissue next to each tumor were examined by electron microscopy. Chrysotile asbestos fiber bundles were found in 3 of the 6 exposed men, all of them with laryngeal cancer. None were found in the two pharyngeal cases, one of which had a wollastonite fiber of uncertain significance. No mineral fibers were found in the comparison case. Every sample was well below the recommended tissue amount, so the authors said cases without fibers should be considered inconclusive rather than negative. The authors concluded that the findings bolster the evidence that asbestos is a risk factor for laryngeal cancer.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Small case series: electron-microscope mineral fiber analysis of tissue next to tumors in selected cancer cases, with one unexposed case as a control
• Who was studied: Six squamous cell carcinoma cases (4 laryngeal, 2 pharyngeal, listed as oropharynx in Table 1) with self-reported occupational asbestos exposure. They were classified as HPV-negative by blood (serologic) testing for antibodies to high-risk HPV proteins. They were selected from a population-based case-control study of head and neck cancer in the Boston area that had occupational histories for 1056 cases, and their tissue was archived at Massachusetts General Hospital. All six were Caucasian males with a median age of 63.5 years (range 56 to 77). One control was a 64-year-old Caucasian male with laryngeal cancer and no occupational asbestos exposure.
• Exposure: Self-reported work in occupations judged high risk for asbestos exposure: autobody repair and automotive mechanic, space shuttle thermal protection applicator, firefighter, Army artillery, school custodian, and metal lather. The median time in an asbestos-exposed occupation was 34.5 years (range 5 to 56). Fibers 5 µm or longer were counted.
• Main results:
  • Chrysotile asbestos fiber bundles were found in tissue next to the tumor in 3 of the 6 asbestos-exposed cases, all of which had laryngeal cancer.
  • Neither of the two HPV-negative pharyngeal cancer cases had detectable asbestos fibers.
  • The chrysotile fibers found ranged from 7 to 14 µm in length and 0.2 to 0.5 µm in diameter.
  • A wollastonite fiber of unclear significance was found in one of the pharyngeal cases.
  • No mineral fibers were found in tissue from the control case without occupational exposure.
  • Tissue samples for all cases were well below the recommended 0.3 g wet weight for fiber analysis. Table 2 lists weights from 0.0001 g to 0.0110 g.
• The authors' conclusion: The authors concluded that finding chrysotile fibers in tissue next to laryngeal squamous cell carcinoma bolsters the mounting evidence that asbestos is a risk factor for laryngeal cancer.
• Limitations the authors state:
  • Because of labor, resource and archival tissue constraints, only a small subset of asbestos-exposed cases could be evaluated.
  • The wet tissue weight was suboptimal for fiber detection, so the authors cannot rule out fibers being present in the cases where none were found.
  • The authors stated that samples with no identifiable asbestos fibers should be considered inconclusive rather than negative.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Throat and laryngeal cancer.

Medical terms in this study, explained in our Lexicon: Chrysotile, Squamous Cell Carcinoma, Asbestos Exposure, Silicate, Mesothelioma, Lung Cancer, Case-Control Study, Mineral Fiber.

Related studies

• Systematic screening for occupations and occupational exposures in head and neck squamous cell carcinoma patients — S. Deneuve, B. Charbotel, et al. (2019)
• Occupational dust exposure and head and neck squamous cell carcinoma risk in a population-based case-control study conducted in the greater Boston area — S.M. Langevin, M.D. McClean, et al. (2013)
• Occupational asbestos exposure as a risk factor for laryngeal carcinoma in a population-based case-control study from Germany — H. Ramroth, W. Ahrens, et al. (2011)
• Occupational asbestos exposure is associated with pharyngeal squamous cell carcinoma in men from the greater Boston area — S.M. Langevin, M.H. O'Sullivan, et al. (2013)
• The history, aetiology and epidemiology of laryngeal carcinoma — M.A. Rafferty, J.E. Fenton, et al. (2001)
• Laryngeal and hypopharyngeal cancer and occupational exposure to asbestos and man-made vitreous fibers: results of a case-control study — J.L. Marchand, D. Luce, et al. (2000)

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