Lobular endocrine neoplasia in fibroadenoma of the breast.

Four cases of endocrine neoplasia within fibroadenomas of the breast are described. The tumours are identifiable by light microscopic, silver impregnation and ultrastructural studies. Argyrophilia and the presence of dense-core granules establish the identity of this tumour type. The differential diagnosis from, and possible relation to, lobular carcinoma in situ are discussed.