Immunohistochemical localization of prekeratin filaments in benign and malignant cells in effusions. Comparison with intermediate filament distribution by electron microscopy.

An immunoperoxidase technique employing antibody to prekeratin was used to study distribution and pattern of staining of prekeratin filaments in cytological smears obtained from 42 specimens of pleural and peritoneal effusions (27 benign, 15 malignant). The smears were either air-dried or ethanol-fixed. Both benign and malignant mesothelial cells showed distinctive peripheral or perinuclear staining patterns which differed from the characteristic arborizing pattern in adenocarcinoma cells. The ultrastructure of these 2 cell types studied in 27 body fluids (12 benign, 15 malignant) and in 13 malignant tumors (3 mesotheliomas, 10 adenocarcinomas) showed a distinctive localizaton of intermediate filaments which corresponded to and could explain the pattern of staining obtained using the immunoperoxidase technique. The immunohistochemical and ultrastructural findings appeared characteristic for benign and malignant mesothelial cells as well as for adenocarcinoma cells, and could be used as markers to differentiate mesothelial tumors and reactive mesothelial cells from adenocarcinomas.