Malignant Mesothelioma and Occupational Exposure to Asbestos: An Analysis of 1445 Cases

Abstract

Asbestos exposure is indisputably associated with the development of malignant mesothelioma (MM). However, relatively few studies have correlated the manner of exposure with asbestos fiber content and type. We report findings from 1445 MMs with known exposure histories, including fiber burden analyses performed in 268 cases. A total of 1445 histologically and immunohistochemically confirmed cases of MM were placed in 23 categories, according to the predominant manner of asbestos exposure. Asbestos body counts were determined by light microscopy. Asbestos fiber content and type were assessed using scanning electron microscopy and energy dispersive X-ray analysis. Ninety-four percent of cases fell into 19 of the 23 exposure categories. Six occupational categories, including pipefitter, boilermaker, machinist, electrician, maintenance worker and sheetmetal worker, as well as one para-occupational (household contact) exposure category, were represented. Twelve categories reflected the kind of industry in which exposure occurred. These included insulation, shipbuilding, railroad, oil/chemical, paper mill, US Navy, molten metal, glass/ceramic, power, automotive, asbestos manufacture and construction. Elevated levels of commercial amphibole fibers were identified in all 19 categories. The highest levels were identified among insulation and asbestos manufacturing industries and pipefitters. The median value of non-commercial amphibole fibers exceeded commercial amphibole fibers in four categories (automotive industry, household contacts, building occupants and environmental exposures). Multiple exposure categories were identified in one-quarter of cases. The majority of MMs in the USA fall into a limited number of exposure categories, with overlap of categories in a substantial proportion of cases. For most exposure categories, commercial amphiboles are the predominant fiber type.