Most
malignant mesothelioma cases are associated with pulmonary
asbestos body (AB) counts significantly greater than those of the general population. However, the question remains whether
malignant mesothelioma cases associated with "normal" AB counts (i.e., indistinguishable from the general population) represent background incidence levels or are, actually,
asbestos related. We performed AB counts (by light microscopy) and
mineral fiber analysis (by scanning electron microscopy) in 18
mesothelioma cases with AB counts within our normal range (0 to 20 AB/G
wet lung) and in 19 "control" cases. Our study demonstrated that approximately one-third (6 of 18) of the
mesothelioma cases have
asbestos fiber burdens greater than 95% of the control levels. These results suggest that these six
mesothelioma cases may be
asbestos related despite AB counts similar to those of the general population. An
asbestos etiology was suggested in three additional cases, but too few
amphibole fibers were identified in these cases to be certain of a value above background. The remaining nine cases showed no evidence of an
asbestos etiology. Electron microscopic analysis of pulmonary
mineral fibers may be required to differentiate
asbestos-related
mesotheliomas from non-
asbestos-related cases when AB counts are within the range of background values.