Epithelial membrane antigen antibody (EMA) belongs to a heterogeneous family of highly glycosylated transmembrane proteins known as human milk fat globule (HMFG) membrane proteins. This family of antigens is not restricted to breast but may also be found in secretory epithelial cells, to a lesser degree, in non-secretory epithelium (e.g., squamous epithelium) and rarely in non-epithelial cells.

Epithelial Membrane Antigen (EMA) is a mucin glycoprotein expressed on apical epithelial cells. Anti-EMA positively stains normal and neoplastic cells including sweat glands, mammary epithelia, and squamous epithelia. Adrenal carcinoma, seminomas, paraganglioma, hepatocellular carcinoma, and embryonal carcinomas exhibit a negative stain. As Anti-EMA commonly reacts positively with meningioma, it is useful for differentiating it from other intracranial neoplasms such as schwannomas. The absence of EMA can also be of value since negative EMA staining is characteristic of some tumors including adrenal carcinoma, seminomas, paraganglioma and hepatoma.