[A study on the tumorigenic process of mesothelioma induced by intrapleural injection of crocidolite in rats].

90 Wistar strain rats were used in this experiment, 56 rats (Group A) were injected intrapleurally with crocidolite fibers suspended in physiological (NaCl) solution. Another 34 rats (Group B), serving as controls, were injected with the same volume of mere NaCl solution. The rats were killed 1, 3, 6, 9, 12, 14 and 16 months respectively after injection. The results showed that the rats of Group B only exhibited reactive proliferation of mesothelial cells caused by inflammation. In Group A, there appeared 9 cases of mesothelioma. The tumorigenic stages of mesothelioma include three processes: (1). reactive proliferation: the mesothelial cells became cuboid. (2). precancerous changes: the atypical proliferation of stratified, nodular or papillary mesothelial cells and of the cell elements around asbestos granulomas. (3). the occurrence of mesothelioma. Ultrastructural observation revealed that in mesothelioma tissue mesenchymal cells directly or indirectly (via transitional cells) differentiated cinto epithelioid cells. The mesenchymal cells may also become fibroblastoid cells. These findings suggest that mesothelioma originates from mesenchymal cells.