HISTOPATHOLOGY AND ULTRASTRUCTURE OF PLEURAL MESOTHELIOMAS PRODUCED IN THE RAT BY INJECTIONS OF CROCIDOLITE ASBESTOS

  • 1 January 1979
    • journal article
    • research article
    • Vol. 60  (6) , 642-652
Abstract
Primary tumors of the pleural cavity were produced in rats by the intrapleural injection of crocidolite asbestos. Their histological structure as seen with light microscopy and EM was very variable and tumors frequently contained elements of connective-tissue and epithelial type tissue. In some instances the connective-tissue elements predominated from the start and the earliest tumor nodules consisted mainly of pleomorphic connective-tissue cells with only a few layers of cells more nearly epithelial in type on the surface. This pattern was largely retained when tumor nodules increased in size and coalesced, but in the deeper layers of advanced tumors the pleomorphic connective-tissue pattern was often replaced by a more uniform spindle-cell form. Other tumors were more predominantly epithelial in type, showing a papillary pattern with rounded epithelial cells growing in solid columns or a vesicular form in which large tissue spaces, often intracellular, were lined by very thin layers of extended cell cytoplasm. Whereas early tumors showed only 1 histological pattern, the more advanced stages often exhibited areas of all 3, so that there seemed to be some degree of histological mutability. The spindle-cell areas of advanced tumors frequently showed evidence of direct invasion of the surrounding tissue but this was never seen with the epithelial forms of rat mesothelioma.