Response to Letter to the Editor on the Mortality of Talc Miners and Millers From Val Chisone, Northern Italy
We thank Dr. Mirabelli for his letter about a patient with pleural mesothelioma who was identified in the Regional Mesothelioma Registry, and allegedly was employed as talc miner and belonged to the cohort whose analysis of mortality during 1946 to 2013 we recently reported in the Journal.1 Dr. Mirabelli was courteous enough to share the personal data of this patient; we double-checked this information against the roster of the cohort and we were not able to identify him. The number of observed deaths from pleural mesothelioma in our cohort remains therefore zero.
We can offer three possible explanations for the discrepancy between the data in our cohort and those in the Mesothelioma Registry. First, this patient might have been employed in graphite production, since a graphite plant, including a mine, was operated in the same alpine valley by the same company that owned the talc mine. We have some records of the workers employed in graphite production, and could not identify the patient. However, contrary to the talc, the graphite records might not be complete and we are not fully confident that this patient had not been employed there. Second, the patient might have been employed by a subcontractor involved in maintenance operations at the talc site; however, we have no data to test this hypothesis. Third, the information on employment available in the Mesothelioma Registry, which was provided by a next-of-kin, might be wrong.
Dr. Mirabelli's statement on the possible contamination of talc by asbestos is contradicted by the available evidence, as we have recently discussed in detail.2 Exposure to asbestos in maintenance jobs is a hypothesis without supporting evidence.
This example stresses the need for a cautious interpretation of the information collected retrospectively—often from next-of-kin, as in this case—on occupational history and circumstances of exposure within the frame of surveillance systems, such as a Mesothelioma Registry.3 While such data might have some value in identifying general patterns and trends at the population level, their validity for assessing exposures of individual patients may be suboptimal.