Argyrophilic carcinoma "carcinoid tumor" of the breast: case report with electron microscopic and immunohistochemical investigations.

A rare primary argyrophilic carcinoma "carcinoid tumor" of the breast in a 48-year-old woman was investigated by light and electron microscopy, and immunohistochemistry. Light microscopy showed the greater part of the tumor to have characteristic histological features of carcinoid tumor and Grimerius' stain revealed the presence of numerous argyrophilic granules in the tumor cells. Numerous neurosecretory granules and bundles of intermediate filaments were observed ultrastructurally in the cytoplasm. In addition, carcinoembryonic antigen (CEA) and neuronespecific enolase (NSE) were detected in the tumor cells using the immunoperoxidase method. From the results, it is speculated that the tumor cells have the ability to produce CEA as well as NSE in the cytoplasm. The observation of ductal spreading in parts of the tumor, and the detection of CEA, suggest the tumor cells to be derived from mammary epithelial cells.