Intrapulmonary mesotheliomas: their identification by tissue culture

Two cases of primary intrapulmonary spindle-celled sarcomas unrelated to the pleura have been studied by electron microscopy, tissue culture and histochemistry. Ultrastructurally both tumors showed some desmosomial unions. The first case showed cytoplasmic filaments, nuclear inclusions, prominent rough endoplasmic reticulum and abundant collagen in the interstitium. The second tumor showed scanty organelles and a paucity of interstitial connective tissue fibers. In spite of their spindle morphology both tumors showed a similar pattern in vitro, growing as an epithelial plaque in the same way as previously described mesotheliomas and related tumors, such as synovial sarcomas. Histochemistry of the tumor mass allowed the identification of most of the cavities which were engulfed alveoli and bronchioli. Both neoplasm were classified as intrapulmonary mesotheliomas. Their relationship to other pulmonary lesions is discussed.