Malignant mesothelioma is a relatively rare
malignancy with a strong association with prior
asbestos exposure. A percentage of cases is not related to
asbestos, and fiber analysis of lung tissue is a useful methodology for identifying idiopathic or spontaneous cases. We have performed fiber analyses in more than 600 cases of
mesothelioma over the past four decades and were interested in looking for trends in terms of fiber types and concentrations as well as percentages of cases not related to
asbestos. Demographic information was also considered including patient age, gender, and
tumor location (pleural vs. peritoneal). The histologic pattern of the
tumor and the presence or absence of pleural plaques or
asbestosis were noted. Fiber analysis was performed in 619 cases, using the
sodium hypochlorite technique for digestion of lung tissue samples.
Asbestos bodies were counted by light microscopy (LM) and coated and uncoated fibers by scanning electron microscopy (EM). The results were stratified over four decades. Trends that were observed included increasing patient age, increasing percentage of women, increasing percentage of peritoneal cases, and increasing percentage of epithelial histological type. There was a decreasing trend in the percentage of patients with concomitant
asbestosis (p < 0.001). The percentage of cases with an elevated lung
asbestos content decreased from 90.5% in the 1980s to 54.1% in the 2010s (p < 0.001). This trend also held when the analysis was limited to 490 cases of pleural
mesothelioma in men (91.8% in the 1980s vs. 65.1% in the 2010s). There was a decrease in the median
asbestos body count by LM from 1390
asbestos bodies per gram of
wet lung in the 1980s to 38 AB/gm in the 2010s. Similar trends were observed for each of the
asbestos fiber types as detected by EM. We conclude that there has been a progressive decrease in lung fiber content of
mesothelioma patients during the past four decades, with an increasing percentage of cases not related to
asbestos and an increase in median patient age.