MORPHOLOGICAL VARIATIONS IN TRANSPLANTED TUMORS DEVELOPED BY INOCULATION OF SPONTANEOUS MESOTHELIOMA CELL-LINES DERIVED FROM F344 RATS

Morphological and immunohistochemical features of the abdominal mesoth eliomas that were developed by inoculation of 3 cell lines (MeET-4, -5 and -6) established from spontaneous abdominal mesotheliomas in male F344 rats. Although the original tumors of three cell lines showed sig ns of epithelioid growth with a predominantly simple papillary pattern , transplanted tumors revealed a variety of morphologic features inclu ding epithelioid with glandular structures, sarcomatous, and a mixture of these components. All tumor cells of transplanted tumors were posi tive for a-smooth muscle actin (ASMA) but almost negative for desmin a s were epithelioid cells of the original tumors, and the cell lines we re positive for desmin but not for ASMA. These results suggested that mesothelioma in the F344 rat had the potential for wide spectrum diffe rentiation under in vitro conditions, The microenvironmental factors o btained in vivo can modify their potential ability and their morpholog ical aspects. These factors may be related to tumor cell reexpression of ASMA of tumor cells that were masked under in vitro culture conditi ons.