Cytologic and tissue culture characteristics of asbestos-induced mesothelioma in rats.

Mesotheliomas were induced in rats by the intrapleural injection of Western Australia crocidolite asbestos. Over a two-year period, 10 of 18 animals in which implants were established developed mesotheliomas, for a 56% success rate. Histologically, most mesotheliomas were biphasic although predominantly spindle celled. Pleural fluid was examined in five of these malignant cases: three had a papillary epithelial picture, one had mainly anaplastic cells, and one contained predominantly spindle-shaped cells. Three types of cell aggregates occurred: classical collagen-containing papillary clusters, spindle-cell aggregates and cystlike spheres. These last structures corresponded to microcystic or adenomatoid growth present in four mesotheliomas. Two of the effusions were cultured successfully; the growth pattern was typically mesothelial, with in vitro production of collagen. Ultrastructurally, long, slender microvilli, cell junctions and intermediate filaments confirmed the mesothelial nature of these asbestos-induced rat malignancies.