Argyrophilic breast carcinomas: evidence of lactational differentiation.

Twenty unselected breast carcinomas were examined for argyrophilia by the Sevier-Munger stain and for dense-core secretory granules by electron microscopy. All cases were examined for lactalbumin and five cases were also studied for gastrin, insulin, calcitonin, somatostatin, glucagon, ACTH, prolactin, and pancreatic polypeptide by an immunoperoxidase technique; two cases were further analyzed for lactalbumin by ultrastructural immunoperoxidase stain. Focal or diffuse argyrophilia was present in ten cases. Intracytoplasmic lactalbumin was present in seven of these cases, but immunoperoxidase staining for the neuroendocrine hormones was negative. Fine structural examination demonstrated varying numbers of 95 to 450-nm-diameter, round, membrane-bound, dense-core secretory granules in 13 cases. Nine of the granule-containing cases were also argyrophilic, and seven of these contained intracytoplasmic lactalbumin. Both the argyrophilia and the dense-core secretory granules thus correlated with the presence of intracytoplasmic lactalbumin. None of the 20 patients had clinical evidence of carcinoid syndrome or showed evidence of other hormone secretion. Argyrophilia and granular lactalbumin staining in a somewhat similar pattern was found in pregnant and lactating breast controls. Argyrophilia and ultrastructural dense-core granules are common in breast carcinomas and might represent lactational differentiation. These findings do not indicate the presence of a carcinoid tumor because in most of these tumors the secretory granules appear to contain milk protein secretory product rather than neuroendocrine polypeptides, and most argyrophilic tumors do not morphologically or clinically resemble carcinoid tumors.