While conventional cytodiagnosis can, in most instances, recognize cancer cells in metastatic effusions from solid tumors, the cellular type or the organ of origin of the primary neoplasia can rarely be determined only on the basis of their morphology. In the present study we have evaluated whether immunocytochemical techniques can be used to overcome this limitation by employing a panel of monoclonal antibodies (MoAbs) to tumor associated antigens (TAA) which lack detectable reactivity with mesothelial cells. To this end we have analyzed, by indirect immunofluorescence, cytospins of 60 malignant effusions of unknown origin. The results of this study have shown that the definition of the origin of the primary tumor, which was subsequently confirmed histologically and/or clinically, could be reached in 87% of the cases. These findings demonstrate that selected combinations of MoAbs, when used in immunocytochemical tests, can provide a powerful diagnostic tool in defining the site of cryptic primary neoplasias causing metastatic effusions.
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