Historical cohort study of US man-made vitreous fiber production workers: II. Mortality from mesothelioma

As part of our ongoing mortality surveillance program for the US man-made v itreous fiber (MMVF) industry, we examined mortality from malignant mesothe lioma using data from our 1989 follow-up of 3478 rock/slag wool workers and our 1992 follow-up of 32,110 fiberglass workers. A manual search of death certificates for 1011 rock/slag wool workers and 9060 fiberglass workers re vealed, only 10 death certificates with any mention of the word "mesothelio ma." A subsequent review of medical records and pathology specimens for 3 o f the 10 workers deemed two deaths as definitely not due to mesothelioma an d one as having a 50% chance of being caused by mesothelioma. Two other dea ths, for which only medical records were available, were given less than a 50% chance Of being due to mesothelioma. Eight of the 10 decedents had pote ntial occupational asbestos exposure inside or outside the MMVF industry. W e also estimated the mortality risk from malignant mesothelioma in the coho rt using two cause-of-death categorizations that included both malignant an d benign coding rubrics. Using the more comprehensive scheme, we observed o verall deficits in deaths among the total cohort and fiberglass workers and an overall excess among rock/slag wool workers. The excess in respiratory system cancer is largely a reflection of elevated lung cancer risks that we attributed mainly to confounding by smoking, to exposures outside the MMVF industry to agents such as asbestos, or to one or more of the several co-e xposures present in many of the study plants (including asbestos). The seco nd scheme, which focused on pleural mesothelioma in time periods when speci fic malignant mesothelioma coding rubrics were available classified only on e cohort death as being caused by malignant mesothelioma, compared with 2.1 9 expected deaths (local county comparison). We conclude that the overall m ortality risk from malignant mesothelioma does not seem to be elevated in t he US MMVF cohort.