1,601 pleural effusions were found to be malignant between 1976 and 1987. Among these were 26 (1.6% of the malignant effusions) mesothelioma. Only 2 cases showed pronounced cytologic features that made a definite diagnosis possible on cytologic criteria alone. In 20 cases diagnosis of mesothelioma was strongly suggested by the patients’ history and cytology of the effusion was compatible with mesothelioma. In the other 4 cases special examinations (histo- and immunohistochemistry, electron microscopy) led to the final diagnosis. The cytologic features of mesothelioma and other examination techniques, needed to resolve the differential diagnosis of mesothelioma versus other neoplasm in pleural effusions, are discussed.

We report two cases of malignant pleural and pericardial effusion respectively secondary to bronchogenic carcinomas. In both effusions, a significant elevation of the Salivary-type-amylase fraction was found, while the corresponding values were normal in serum and urine. Electronmicroscopy of the malignant tumor cells from the pleural effusion showed typical electron-dense granules, suggesting zymogen granules. It is concluded that the high amylase content of the effusions was due to secretion of S-type-isoamylase by the tumor cells.

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Spleen from normal BALB/c, DBA/2 and C3H mice exerted a protective effect against syngeneic and allogeneic cell‐free transmission of HIPA plasmacytoma in mice. The maximal protective effect of these spleens was found in C3H and ICR mice (100‐70%). Inoculation of BALB/c spleen homogenates in syngeneic mice resulted in protection of about 56% of the cases. Spleen homogenates from BALB/c mice were not effective against cellular transplantation of HIPA plasmacytoma. The fact that the protection required one week to develop suggested that an immune reaction was involved. The factor responsible for protection was found in the sedimentable fraction of spleen homogenates centrifuged at 500 × g during 15 minutes and was destroyed by heat and freezing/thawing.