Intracystic papillary carcinoma of the male breast. Immunohistochemical and ultrastructural study.

We report a case of mammary intracystic papillary carcinoma occurring in a 75-year-old man. The tumor was present on the left pectoral area for five years. Grossly, the neoplasm was a cystic structure 10 cm in diameter, with multiple intramural filiform papillae and small foci of cyst wall invasion. By transmission electron microscopy the tumor cells had the normal complement of organelles and also multiple electron-dense, membrane-bound secretory granules. These granules were also demonstrated with multiple stains for argyrophilia and with periodic acid-Schiff. Immunoperoxidase stains were negative for neuron-specific enolase, S100 protein, vasoactive intestinal peptide, corticotropin, calcitonin, lactalbumin, and bombesin, and positive for human heart factor (myoepithelial cells) and carcinoembryonic antigen. We believe that this rare neoplasm represents a variant of mammary adenocarcinoma and not a neuroendocrine (carcinoid) neoplasm.