[GC12, marker of cells of mesodermal origin. Value and application to cytodiagnosis of serous effusions].

Monoclonal antibody GC12 was examined for its value in cytopathologic diagnosis. Its sensitivity and specificity in staining reactive mesothelial cells in serous effusions was determined using the indirect immuno alkaline phosphatase anti-alkaline phosphatase technique. Smears prepared from 78 serous effusions (15 benign, 54 malignant, 9 atypical) were immunostained with GC12 and five other monoclonal antibodies: KL1 directed against cytokeratins, D33 against desmin, E29 against epithelial membrane antigen, Calam 27 against epithelial surface antigen and NEO 723 reactive with carcinoembryonic antigen. GC12 reacted positively with 80 to 100% mesothelial cells from the 15 benign effusions. Carcinoma cells were negative in 87% of malignant cases. Ovarian carcinomas were specially stained among positive cases. One malignant mesothelioma was positive and one was unreactive with GC12. Moreover, the reactivity of atypical cells in 9 serous effusions with GC12 was helpful to characterize benign and malignant effusions: the immunophenotype GC12-, Desmine-, Calam 27+, EMA+, ACE+ allowed detection of carcinoma cells in 2 cases. It is concluded that GC12 is a good tool for distinguishing carcinoma cells from reactive mesothelial cells in serous effusions.