Papillary neoplasia of the breast: immunohistochemically defined myoepithelial cells in the diagnosis of benign and malignant papillary breast neoplasms.

The presence or absence of myoepithelial cells (ME) has been considered as an important feature in the differential diagnosis of benign and malignant papillary lesions of the breast. We evaluated the distribution of myoepithelial cells in formalin-fixed paraffin-embedded tissue sections of 25 papillomas and 18 papillary carcinomas by ABC immunoperoxidase technique with antibodies to muscle actin (HHF-35) and high molecular weight (HMW) keratin (clone 34BE12, cytokeratins 1, 5, 10, and 14; reacting preferentially with ME cells) and an antiserum to S-100 protein. Also included in the study were eight cases of micropapillary ductal carcinoma in situ (DCIS) having a few fibrovascular cores and five peripheral papillomas with accompanying ductal carcinoma in situ or atypical hyperplasia. The antibodies to muscle actin were sensitive and relatively specific for ME cells of the breast and uniformly labeled ME cells in all 25 papillomas. ME cells were absent or extremely sparse in papillary carcinomas. They were present focally in some of the fibrovascular cores of the micropapillary DCIS, and a mixed pattern was observed in peripheral papillomas with areas of carcinoma. HMW keratin was variably expressed in ME cells in most cases with positive internal controls and was present in several normal ductal and papilloma epithelial cells but not in epithelial cells of papillary carcinomas. HMW keratin, although less specific for ME cells, was a useful adjunct because of its reactivity with ME cells as well as hyperplastic epithelial cells in papillomas, which resulted in a combined positive reaction.(ABSTRACT TRUNCATED AT 250 WORDS)