The "missing cases" of pleural malignant mesothelioma in Minnesota, 1979-81: preliminary report

Malignant mesothelioma is a sentinel neoplasm for population exposure to asbestiform fibers. Public health officials may be alerted to temporal or spatial clustering of malignant mesothelioma through analyses of vital records, such as death certificates. Hence, the maintenance of the integrity of the vital statistics system, particularly the cause of death statement on the death certificate, is very important. The report by a northeastern Minnesota radiologist in January 1985 of an elevated prevalence of pleural plaques (related to asbestiform fiber exposure) to the Minnesota Department of Health resulted in an investigation of pleural malignant mesothelioma mortality trends in that area and in three other similar areas in the State. In that study, we noted that in several instances malignant mesothelioma (either intrathoracic or unspecified site) was listed on the death certificate in such a manner as to imply that the neoplasm was either a lung cancer or a malignancy of an unspecified site. The effect of this misclassification is to underestimate the mortality from malignant mesothelioma by fourfold to eightfold. Given the importance of malignant mesothelioma as a proxy for past asbestos exposure, it is necessary to determine the extent of such misclassification for all deaths in the United States.