They hypothesized that no threshold burden of asbestos fibers is needed to produce mesothelioma. Mesothelioma occurs in some people with low exposure.18,19 Other reports have suggested that a dose-response relationship exists.20,21 Tuomi et al22 studied lung asbestos content from 23 people with mesothelioma and correlated the findings with occupational history of asbestos exposure. They determined that asbestos burden correlates with work exposure. In 2 cases, no ferruginous bodies were identified in sections or after tissue digestion. Biphasic mesotheliomas contain regions with an epithelial pattern and regions with a sarcomatous pattern.
Tumors tend to be variable in their histologic pattern.
As pointed out by Hammar,7 the more tumor available for examination, the more variation will be seen. As discussed by Hammar,7 diffuse mesotheliomas encase the lung and can encase mediastinal structures. The esophagus, trachea, heart, and great vessels may become involved by tumor. Lung parenchymal invasion is common. Metastases may occur in lymph nodes associated with the hilum and mediastinum, as well as in the lung parenchyma.