34 beta E12 cytokeratin immunodetection in the differential diagnosis of neuroendocrine carcinomas of the breast

Neuroendocrine (NE) carcinomas of the breast share morphologic and immunohi stochemical features with NE tumors of other sites, either resembling typic al carcinoids or the highly aggressive small cell carcinoma. In addition, s ome mucinous carcinomas or solid/papillary carcinomas may show a major NE c omponent. This is generally recognized by specific immunodetection of pan-e ndocrine markers, although this approach may fail to recognize NE tumors la cking immunoreactivity for some NE products, because the antigen is produce d but not retained in the cytoplasm. It has recently been reported that hig h molecular weight (HMW) cytokeratin (CK), recognized by clone 34 beta E12, immunostaining selectively labels non-NE carcinomas (squamous-cell and ade nocarcinomas) of the aerodigestive tract and lung. The role of such CK immu nodetection in the differential diagnosis of NE carcinoma of the breast was evaluated. Twenty-four cases of breast carcinomas having NE differentiatio n were selected. Twenty-four cases of non-NE invasive breast carcinomas ser ved as controls. HMW CK immunoreactivity was found in all but one case of n on-NE carcinomas, but in only two NE tumors (having scattered positive cell s only). The authors conclude that in breast carcinomas the presence of HMW CK immunoreactivity favors the diagnosis of non-NE carcinoma, whereas its absence supports that of a NE tumor (either a carcinoid or a small cell car cinoma or a mucinous carcinoma). HMW CK can be added to the list of markers useful in the differential diagnosis of NE from non-NE tumors.