Keratin and carcinoembryonic antigen in exfoliated mesothelial and malignant cells: an immunoperoxidase study

Immunoperoxidase technics were used to identify keratin and carcinoembryonic antigen (CEA) in exfoliated cells of fine-needle aspirates and body cavity fluids. Staining was evaluated in cytocentrifuge preparations from 27 malignant and 30 benign cytologic specimens. Most reactive mesothelial cell preparations were strongly positive for keratin and negative or only weakly positive for CEA. Diffuse, peripheral, and perinuclear concentration of staining for keratin was noted in exfoliated reactive mesothelial cells. Positive staining for keratin, predominantly diffuse, was noted in exfoliated cells from 56% of the adenocarcinomas. Sixty-nine per cent of adenocarcinoma preparations were strongly positive for CEA. These findings suggest that keratin proteins are not restricted to squamous cells and that keratin staining does not permit distinction between adenocarcinoma and mesothelial cells in cytologic specimens. Staining for CEA and keratin was compared in cytocentrifuge preparations and histologic sections of 12 adenocarcinomas and 7 lymphomas. In some adenocarcinomas, staining was detected only in cytologic preparations. Possible explanations for these differences are discussed. Variable staining for keratin was observed among exfoliated reactive mesothelial cells, possibly identifying different mesothelial cell populations. All reactive and neoplastic lymphoid cells were negative for keratin and CEA in cytologic and histologic preparations. Immunoperoxidase technics can be applied to rehydrated Papanicolaou-fixed and Papanicolaou-stained cytologic preparations with excellent preservation of cytologic detail.