ORIGINAL ARTICLE

Mesothelioma in Occupational Cohort Studies Methodological Considerations Nancy C. Wojcik, MS, A. Robert Schnatter, PhD, and Wendy W. Huebner, PhD

Objective: This article describes effective strategies for the identification and valid assessment of mortality due to mesothelioma. Methods: We manually reviewed all death certificates for mention of mesothelioma for all International Classification of Diseases (ICD) revisions. We tested the accuracy of our ascertainment method by comparing New Jersey death certificate data from our health status registry with histologically confirmed cases from the New Jersey State Cancer Registry. Results: We found reasonably good agreement between death certificate diagnoses and histologically confirmed cases, κ coefficient 0.86 (95% confidence interval, 0.76 to 0.95). Most mesothelioma deaths in our test and North American cohorts were coded to unspecified anatomical sites. Conclusions: Limiting ascertainment to pleura and peritoneum ICD codes underestimates mesothelioma deaths. Reviewing all ICD codes that could contain mesothelioma is the only effective method for complete capture of mesothelioma diagnoses.

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esothelioma is a cancer of the mesothelial cells, which form thin membranes that line the cavities of the chest (pleural), abdomen (peritoneal), heart (pericardium), and the surface of most organs.1 The most common anatomical site for malignant mesothelioma occurrence is the pleura, followed by the peritoneum.1 Malignant mesothelioma is primarily associated with occupational exposure to airborne asbestos1,2 and is known for its long latency of 20 to 40 years between exposure and appearance of disease.2–4 In the United States, occupational exposure to asbestos increased during World War II, most notably in shipbuilding, asbestos product manufacturing such as insulation, and construction operations.5,6 After peak use in the 1950s5,7 through the early 1970s, asbestos consumption declined over the next several decades2,4,6 as awareness of the hazard increased. In many petroleum refineries, asbestos was used for thermal insulation, as a gasket material, and as protective screening during welding operations. These uses changed in the United States in the mid- to late-1960s when refineries began to replace asbestos with other materials. Recognizing the potential hazard from asbestos exposure in earlier eras and the long latency of mesothelioma, we and others have conducted several cohort mortality studies to monitor mesothelioma risk in petroleum industry workers. Studies of early era petroleum industry workers in the United States and elsewhere8–18 report a 2- to 5-fold elevation in mesothelioma mortality with higher risks among subgroups of maintenance workers.9,10,13,15 Most decedents were hired in the 1950s or earlier, worked in refineries as insulators or pipefitters, and had long job tenure and latency (some 40 to 50+ years). From ExxonMobil Biomedical Sciences, Inc (Ms Wojcik and Dr Schnatter), Epidemiology & Health Surveillance, Annandale, NJ; and Independent Consultant, Epidemiologist (Dr Huebner), Montclair, NJ. ExxonMobil has sponsored this research. Nancy C. Wojcik and A. Robert Schnatter are currently employed by ExxonMobil Biomedical Sciences, Inc. Wendy W. Huebner was previously employed by the same company. Address correspondence to: Nancy C. Wojcik, MS, ExxonMobil Biomedical Sciences, Inc, Epidemiology & Health Surveillance, 1545 US Hwy 22 E, Annandale, NJ 08801 ([email protected]). C 2013 by American College of Occupational and Environmental Copyright  Medicine DOI: 10.1097/JOM.0000000000000059

Given mesothelioma’s long latency, continued surveillance among petroleum industry workers is warranted. Additional information can contribute to understanding the potential risk among workers hired after 1950 as they accumulate more follow-up time. Surveillance can also provide signals related to the effectiveness of current asbestos controls and signals related to potential risks from deterioration of contained asbestos and exposures to nonasbestos sources such as nanoparticles, which have not been well-studied.2,19 Accurate surveillance relies on the completeness of mesothelioma case capture. This is inherently difficult when studying mesothelioma mortality. First, mesothelioma lacked a specific causeof-death code until the Tenth Revision of the International Classification of Diseases (ICD). In earlier ICD revisions, mesothelioma cases could be coded under other anatomical cancer sites. For example, in the ICD-9, mesothelioma cases could be coded as 158.9 for peritoneal cancer, 162.9 for lung cancer, 163.9 for pleural cancer, and 199.1 for cancer of unspecified or other sites. Nevertheless, these codes are not specific to mesothelioma. Second, because of the lack of specific coding, there are no national death rates for mesothelioma before 1999, making it difficult to assess patterns and trends of mesothelioma mortality among the general population, which frequently serve as the comparison population for worker cohorts. These challenges have been acknowledged by others.6,20–25 Several studies have investigated the accuracy between histologically confirmed mesothelioma diagnoses and death certificate cause-ofdeath data to assess how well mesothelioma is captured using ICD codes.21,22,25,26 It is clear from these studies that relying on the ICD codes for malignant neoplasms of both the pleura and peritoneum fails to capture all malignant mesotheliomas.21,22,25,26 In the 1970s, investigators began applying modern life table techniques to study mortality in petroleum workers.27,28 Software used at the time29,30 did not tabulate expected numbers for mesothelioma, cancer of the pleura, and cancer of the peritoneum, because these outcomes were not included in the programs’ default mortality rates. Thus, in early studies, mesothelioma deaths were interspersed among results for several default causes such as cancer of the lung and bronchus, other respiratory cancer, other digestive system cancer, benign neoplasms, and cancer of unspecified site (ICD-8 code 199). The first study to examine mesothelioma and document an elevation (2.4-fold) in petroleum workers was reported in 1986, although ascertainment procedures were not detailed in this report.8 The first study to clearly document mesothelioma ascertainment procedures in a petroleum worker cohort9 was published shortly later, but case ascertainment procedures are not always specified in subsequent research.10–16 In this article, we describe our methods for more complete case capture and present results regarding the distribution of mesothelioma deaths by ICD code from two large cohort studies of men in North American operations. To test the accuracy of our ascertainment method, we compared New Jersey death certificate data from our company’s health status registry with histologically confirmed cases from the New Jersey State Cancer Registry (NJSCR). The methods described ensure complete capture of mesothelioma diagnoses for comparison to mesothelioma incidence rates.

JOEM r Volume 56, Number 1, January 2014 Copyright © 2013 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

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JOEM r Volume 56, Number 1, January 2014

Wojcik et al

METHODS Mesothelioma Death Ascertainment For mesothelioma death ascertainment, we conduct a manual review of all death certificates for any mention of mesothelioma. In this company, the practice of manually reviewing each death certificate for mention of mesothelioma was implemented in the late 1980s. A nosologist, trained by the National Center for Health Statistics, developed a comprehensive list of ICD-7, ICD-8, and ICD9 codes that could possibly contain a diagnosis of mesothelioma. Table 1 lists the ICD codes that we recognize as possible mesothelioma codes from the ICD-7, ICD-8, and ICD-7, as well as the recent ICD-10, that established specific, all inclusive codes for mesothelioma. The nosologist ascertains mesothelioma occurrence by manual review of the underlying and contributory causes on death certificates for any mention of mesothelioma. The nosologist then applies ICD rules using the revision in effect at the time of death to determine underlying cause-of-death codes (Table 1). For all death records identified as mesothelioma, a mesothelioma flag is assigned in the company’s health status registry system—a computerized system containing demographic, job, and mortality information for former and current US-based employees.31

Test for Agreement To test for accuracy of our ascertainment method, we compared the New Jersey death certificate data from our health status

TABLE 1. Possible Mesothelioma Cause of Death ICD Codes Used in Company Cohorts

ICD Revision (Date in Effect) ICD-7 (1958–1968)

ICD-8 (1968–1978)

ICD-9 (1979–1998)

ICD-10 (1999–2000)

Malignant Mesothelioma ICD Codes (Anatomical Site) 158 (peritoneum) 163 (lung or pleura) 164 (mediastinum) 197 (site unspecified) 158.9 (peritoneum) 162.1 (lung) 163.0 (pleura) 163.1 (mediastinum) 171.1 (diaphragm) 199.1 (site unspecified) 158.9 (peritoneum) 162.9 (bronchus and lung) 163.9 (pleura) 164.9 (mediastinum) 171.4 (diaphragm) 199.1 (site unspecified) C45 (mesothelioma)

Benign Mesothelioma ICD Codes (Anatomical Site)

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RESULTS Test for Agreement

211 (peritoneum) 212 (lung. pleura, mediastinum) 227 (unspecified) 211.7 (peritoneum) 212.3 (lung) 212.4 (pleura) 212.5 (mediastinum) 215 (diaphragm) 228 (site unspecified) 211.8 (peritoneum) 212.3 (bronchus and lung) 212.4 (pleura) 212.5 (mediastinum) 215.4 (diaphragm) 229.9 (site unspecified) D19 (mesothelial tissue) D48.4 (unknown/ uncertain behavior peritoneum)*

*Recently added behavior code for review for “cystic mesothelioma” in future cohort updates. ICD, International Classification of Diseases.

registry with histologically confirmed mesothelioma cases from the NJSCR. For the test cohort, we selected all male decedents in the health status registry with a New Jersey death certificate and year of death between 1979 and 2000. The death certificate and demographic data were obtained through company benefits and human resources. The decedents include members from previous company cohort studies, as well as more recent employees from all US business segments of the company. The period of time reflects the first year of available state/national cancer information (1979) to the last year of complete company death ascertainment (2000) in our latest published cohort study.32 Cause-of-death information, including underlying and secondary causes of death, was reviewed to distinguish mesothelioma deaths from all other causes of death. Linkage was performed by NJSCR staff using AUTOMATCH probabilistic linkage software (MatchWare Technologies, Inc., Kennebunk, ME). Decedents were matched to NJSCR data, using social security number, name, sex, date of birth, and race (Fig. 1). Company and NJSCR personnel manually reviewed matching results, using cancer site, cancer subgroup, histology codes, pathological findings, and dates of diagnosis, for case verification. Work location information within 5 years of death was included in the study database to help verify one type of nonmatch, that is, a person who died in New Jersey during the study period but who may have lived elsewhere when diagnosed with mesothelioma and later had an unspecified cause of death code on the New Jersey death certificate. On completion of matching, name, social security number, day of birth, and day of diagnosis fields were deleted. Study identity numbers for the analytic file were randomly assigned to each study member. The protocol was approved by the University of Medicine and Dentistry of New Jersey institutional review board.

More than 330,000 US employee records in the health status registry were searched to construct the company test cohort. The test cohort consisted of 3834 male decedents with New Jersey death certificates from 1979 through 2000. Of these, 28 had been flagged as mesothelioma. For the 28 company-identified mesothelioma diagnoses, 57% of the deaths occurred before 1990 (Table 2). Most decedents (75%) were older than 64 years, and 60% died within 12 months of diagnosis (Table 2). Test cohort diagnoses were matched to 917,190 cancer cases diagnosed between 1979 and 2000 by the NJSCR. The results showed that 24 of the 28 company-identified mesothelioma deaths (cohort) were histologically confirmed as mesothelioma cancer cases by the NJSCR (Table 3). Four cohort mesothelioma death certificate diagnoses did not match the NJSCR. Among these four, one decedent died during the first year of the NJSCR registration, so no earlier NJSCR records exist to help examine the accuracy of the death certificate diagnosis. Two decedents had records in the NJSCR shortly before their deaths but did not include mesothelioma cancer diagnosis. The fourth decedent did not have any NJSCR records and died well into the NJSCR catchment period. The absence of any NJSCR records along with the death certificate diagnosis of 199.1 (site unspecified) makes it difficult to confirm the accuracy of the lack of mesothelioma diagnosis on this death certificate. Overall, given the rapid progression of this disease, it is possible that a finite number of cases may not have been accurately diagnosed before death and would not have a registered mesothelioma diagnosis. Confidentiality procedures prevented further investigation of these four nonmatches. Four other cohort death certificates did not contain a mesothelioma diagnosis but did have microscopic confirmation as malignant

 C 2013 American College of Occupational and Environmental Medicine

Copyright © 2013 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

JOEM r Volume 56, Number 1, January 2014

Mesothelioma Cohort Study Methodology

NJSCR diagnosis of mesothelioma? Death certificate diagnosis of mesothelioma

Company cohort male decedents with New Jersey death certificate from 1979–2000

FIGURE 1. Summary of agreement tests between mesothelioma coded death certificates and NJSCR records. NJSCR, New Jersey State Cancer Registry.

Death certificate diagnosis of all other causes

TABLE 2. Demographic Characteristics of Test Cohort; Male Decedents With Malignant Mesothelioma Diagnosed on New Jersey Death Certificates From the Health Status Registry, 1979–2000

Variable

Total Test Cohort (n = 28), %

Matched to NJSCR (n = 24), %

57 43

58 42

25 21 39 36

25 25 42 33

60 25 14

54 29 17

Year of death 1979–1989 1990–2000 Age at death, yr 45–64 55–64 65–74 75+ Months between diagnosis and death

Mesothelioma in occupational cohort studies: methodological considerations.

This article describes effective strategies for the identification and valid assessment of mortality due to mesothelioma...
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