Application of immuno-electron microscopy to the cytologic study of benign and malignant mammary lesions. With special reference to the carcinoembryonic antigen localization patterns.

We investigated the application of immuno-electron microscopic (EM) observation of carcinoembryonic antigen (CEA), one of the surface markers of neoplastic epithelium, to the cytologic diagnosis of mammary cells in smears and imprints. Smears were stained by the indirect peroxidase-labeled antibody method after a modified Karnovsky fixation (4% paraformaldehyde containing 0.05% glutaraldehyde). In smears, CEA was immunocytochemically demonstrated on the entire cell membrane of malignant mammary cells whereas CEA was observed only on microvillous surfaces of benign mammary cells. Another characteristic immunocytochemical feature of malignant cells was the appearance of so-called intracellular lumina, of which the microvillous surfaces were CEA positive. These findings demonstrated that electron microscopic observation of the immunocytochemical localization of CEA is a quite useful tool for the cytologic diagnosis and characterization of neoplastic mammary lesions.