Argentaffin endocrine carcinoma (carcinoid) of the pancreas with concomitant breast metastasis: an immunohistochemical and electron microscopic study.

A pancreatic carcinoid tumor that metastasized to the breast is reported. The breast tumor was originally diagnosed as adenocarcinoma of the breast. Silver impregnation revealed the presence of argentaffin cytoplasmic granules. Immunocytochemical studies demonstrated immunoreactivity for serotonin but not for lactalbumin, a marker for breast epithelial cells. These features, together with the electron microscopic observation of pleomorphic secretory granules, permitted recognition of the tumor as metastatic carcinoid. This report illustrates the importance of the combined histochemical, immunocytochemical, and electron microscopic studies of breast tumors with a carcinoid pattern.