Introduction to Article on Asbestos Job Exposure Using Matrices Reveal Incidence of Asbestos Job Exposure and Cancer

INTRODUCTION

Malignant mesothelioma arises from the lining cells of the coelomic cavities [Mack, 1995]. Malignant mesotheliomas of the pleura and the peritoneum share exposure to asbestos as the major etiologic factor [Spirtas et al., 1994].

However, they differ in respect to sex-ratio, route of exposure (inhalation vs. ingestion) [Mack, 1995], and fiber type (chrysotile vs. amosite asbestos) involved [Peto et al., 1995; Ribak et al., 1989]. In contrast with pleural mesothelioma, which predominates among men, mesothelioma of the peritoneal cavity occurs with roughly equal frequency in men and women [Mack, 1995]. This could imply that the pertinent exposure is distributed with little reference to gender. The geographical pattern of peritoneal mesothelioma in the United Kingdom parallels the past distribution of the asbestos industry, but unlike pleural mesothelioma, it did not cluster in seaports where shipbuilding and ship repairing were carried out [Gardner et al., 1985]. The contrasting features of peritoneal and pleural mesothelioma suggest that different routes of exposure to asbestos and/or different fiber types can contribute to distinct epidemiologic patterns [Leigh et al., 1991].

The underlying cause of death in death certificates is coded using the International Classification of Diseases, 9th revision (ICD-9), which does not single out mesothelioma from the rest of peritoneal cancers. Besides, the proportion of mesothelioma among all peritoneal tumors is unclear. In a recent review of SEER incident data, cancer of the peritoneum was only considered jointly with cancer of the retroperitoneum [Mack, 1995]. Mesothelioma accounted for about 20% of these two cancer sites combined and it did not vary by gender. However, the proportions of epithelium-derived cancers (including mesothelioma) and connective and other soft tissue-derived cancers might be different between the peritoneum and the retroperitoneum. Nevertheless, a recent study in the UK demonstrated that mortality from asbestosis was more closely related to that from peritoneal cancer than pleural cancer [Coggon et al., 1995], which supports using mortality data to explore the association between asbestos exposure and peritoneal cancer.

The same report illustrated that the risks for cancers of the pleura and peritoneum distribute quite differently by occupation, with construction workers being at much higher risk for peritoneal cancer than pleural cancer, vehicle body builders and plumbers showing excesses at both sites, and various other occupations, such as metal plate workers, upholsterers, electricians, and welders showing only pleural cancer excesses [Coggon et al., 1995].

To further investigate the association of peritoneal cancer and occupational exposure to asbestos by gender and to explore the reliability of both a priori designed job exposure matrices and occupational information in the death certificate, we conducted a case-control study using data from a national surveillance program of occupational diseases developed since 1984 by the National Cancer Institute, the National Institute for Occupational Safety and Health, and the National Center for Health Statistics [Burnett and Dosemeci, 1994]. We first designed a job-exposure matrix based on the 1980 U.S. Census list of occupations and industries, and subsequently applied it to the codes on the death certificates of cases and controls.