ASBESTOS CONTAMINATION IN PARAFFIN TISSUE BLOCKS

Electron microscopic analyses of tissue samples embedded in paraffin a re routinely performed as a means of validating (establishing) the asb estos exposure of persons diagnosed with mesothelioma, a rare form of cancer often identified as being caused by exposure to asbestos. Durin g analysis of tissue samples claimed to contain asbestos, we observed asbestos contamination in the paraffin of the tissue block. To investi gate the extent to which such contamination is prevalent in tissue blo ck samples, we obtained and analyzed samples of paraffin blocks from h ospitals in six major cities and found them to contain measurable conc entrations of asbestos. Whether this asbestos contamination originated in the virgin wax or was a result of processing has not been establis hed. This result, which has not been previously reported, raises signi ficant concerns about the validity of analyses for asbestos in tissue embedded in paraffin. In particular, diagnoses in which the presence o f asbestos in tissue samples is taken as being indicative of past asbe stos exposure, especially for those cases in which no known exposure h as occurred, and studies purporting to show migration of asbestos to o ther organs in the body following inhalation or ingestion of asbestos require critical reevaluation. The need for reevaluation is particular ly acute if appropriate control blanks were not evaluated as part of t he studies.