MALIGNANT MESOTHELIOMA ASSOCIATED WITH LOW PULMONARY TISSUE ASBESTOS BURDENS - A LIGHT AND SCANNING ELECTRON-MICROSCOPIC ANALYSIS OF 18 CASES

Most malignant mesothelioma cases are associated with pulmonary asbest os body (AB) counts significantly greater than Obese of the general po pulation. However, the question remains whether malignant mesothelioma cases associated with ''normal'' AB counts (i.e., indistinguishable f rom the general population) represent background incidence levels or a re, actually, asbestos related. We performed AB counts (by light micro scopy) 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 th at approximately one-third (6 of 18) of the mesothelioma cases have as bestos fiber burdens greater than 95% of the control levels. These res ults suggest that these six mesothelioma cases may be asbestos related despite AB counts similar to those of the general population. An asbe stos etiology was suggested in three additional cases, but too few amp hibole fibers were identified in these cases to be certain of a value above background. The remaining nine cases showed no evidence of an as bestos etiology. Electron microscopic analysis of pulmonary mineral fi bers may be required to differentiate asbestos-related mesotheliomas f rom nonasbestos-related cases when AB counts are within the range of b ackground values.