"Carcinoid" tumor of the breast. A variant of conventional breast cancer?

A breast tumor with the morphologic features of a carcinoid tumor and containing large amounts of estrogen receptor protein was associated with areas of typical in situ and infiltrating lobular carcinoma. The carcinoid areas were argyrophilic and ultrastructurally contained electron dense granules on which silver grains were localized. Of 21 other examples of ordinary breast cancer, five showed histologic similarities to carcinoid tumors. Focal argyrophilia was observed in 11 invasive tumors. The presence of argyrophilic granules could not be correlated with the presence of "neurosecretory" granules, although groups of such granules were found in one case of in situ lobular carcinoma. Argyrophilic and "neurosecretory" granules imply the presence of hormonal substances, although in breast tumors these granules have not yet been chemically or immunochemically characterized. Until such evidence becomes available it would appear that most cases reported as primary carcinoid tumors of the breast have much more in common with conventional breast cancer than with the usual carcinoid tumor. Within this context it can be acknowledged that some breast cancers may focally exhibit a carcinoid-like differentiation.