The cytologic diagnosis of mesothelioma.

The cytologic features of malignant mesothelioma cells in serous effusions are presented. Carcinomatous mesotheliomas are characterized by abundant neoplastic cells occurring singly and in clusters. The optically dense cytoplasm with lacy peripheral vacuoles, scalloped borders of cell clusters, intercellular spaces, "cell-in-cell" arrangement, and frequent multinucleation of cells are features of malignant mesothelioma, but none is pathognomonic of this tumor. A positive cytoplasmic staining of tumor cells with periodic acid-Schiff (PAS) after diastase digestion, and with mucicarmine stain after hyaluronidase treatment are against the diagnosis of mesothelioma, while positive staining with alcian blue, which becomes negative after the treatment with hyaluronidase is strongly suggestive of mesothelioma. The tumor cells react with antibodies to cytokeratin and vimentin, and do not react with carcinoembryonic antigen. Ultrastructurally, mesothelioma cells are characterized by long slender branching microvilli and numerous pinocytotic vesicles. They lack mucin vacuoles and intracellular lumens. An accurate diagnosis of mesothelioma depends on a full knowledge of the clinical history and radiologic findings, and proper application of histochemical, immunodiagnostic, and electron microscopic techniques.