Epithelial markers for paraffin-embedded human tissues. Immunohistochemistry with monoclonal antibodies against milk fat globule antigens.

About 200 human tumours and corresponding normal tissue samples were investigated by immunoperoxidase tests for the expression of MAM-3, MAM-5 and MAM-6 antigens, which had previously been defined by monoclonal antibodies to human milk fat globule membranes. All tissue specimens had been treated for routine histopathology, i.e. fixed in formalin and embedded in paraffin. One of the antigens, MAM-6, appeared to be an important epithelial marker, present in all normal and neoplastic breast tissue samples, in about 80% of non-mammary normal tissues and in more than 90% of non-mammary epithelial tumours. It could never be detected in normal and neoplastic mesenchymal and neuroectodermal structures. Direct comparison with the distribution of Carcinoembryonic Antigen (CEA), Tissue Polypeptide Antigen (TPA) and keratin provided clear evidence that MAM-6 is different from these well known epithelial markers. MAM-3 proved to be an additional important marker exhibiting a characteristic distribution pattern in those epithelial tissues investigated. In contrast to MAM-6, it could never be detected in renal cell cancers and carcinomas of the prostate gland, thus allowing differential diagnosis on the basis of immunohistochemistry. MAM-5, known to be associated with lactoferrin, was mainly detectable in secretory organs and their tumours. In the group of breast tumours, its expression was mainly seen in lobular cancers. These findings suggest a use for these new markers for routine histopathology.