Immunocytochemical identification of carcinomas of unknown primary in serous effusions

Metastases from carcinomas of unknown primary site (CUP) in serous effusion are a common clinical problem. Immunocytochemistry was applied as an adjunct to the cytological diagnosis of metastatic carcinomas in serous effusions. Subjects of this study were 118 pleural, 53 peritoneal, and 9 pericardial effusions from 180 patients routinely investigated in the Institute of Cytopathology. Specimens were primarily stained according to Papanicolaou (Pap). The avidin-biotin-complex method (ABC) was secondarily applied for the visualization of immunologic reactions. We have used a panel of six monoclonal antibodies (CK 5/6, CK 7, CK 20, CA 125, TTF-1, and cdx 2) so as to identify the primary tumor site of metastatic carcinoma cells in serous effusions. Applying an algorithm of immunocytochemical marker constellations, we were able to correctly diagnose primary tumor sites in 86 of 101 (85.1%) patients with CUP syndromes. The best result was achieved for the identification of metastatic carcinomas of the ovaries (94.7%) and the lungs (88.1%). We established an algorithm comprising six immunocytochemical markers that enabled a correct diagnosis of primary tumor sites in 85.1%. The panel studied could be useful in diagnostic routine for the identification of primary tumors of unknown origin metastatic to the serous membranes.