An assessment of the value of epithelial membrane antigen and other epithelial markers in solving diagnostic problems in tumour histopathology.

Using standard immunohistological techniques on formalin-fixed paraffin-embedded sections, we have evaluated the role of epithelial membrane antigen in the histopathological diagnosis of tumours. Of the 70 samples examined, 22 were taken for staging purposes from patients known to have carcinoma and, in half these cases, malignant cells were seen which could not be identified with confidence by conventional means. Forty-eight tumours were stained in order to determine their histogenesis. Twenty-two of these were positive and 20 subsequently proved to be epithelial on follow-up studies, including six in which a diagnosis of non-epithelial malignancy had been made on conventional preparations. The distinction of anaplastic carcinoma from malignant lymphoma and of spindle-cell carcinoma from sarcoma were the most useful applications. One of the positive tumours was of germ cell origin and in one the histogenesis is still not clear. Comparison with carcinoembryonic antigen and pre-keratin showed that epithelial membrane antigen was the most sensitive marker of epithelial differentiation in formalin-fixed tissue. A combination of all three reagents, though, increases diagnostic accuracy and allows tentative suggestions to be made about the possible site of origin of a metastatic carcinoma.