Epithelial Proliferative Lesions and Carcinomas in Fibroadenomas of the Breast.

Sixteen cases of fibroadenomas with epithelial proliferative lesions (EP lesions) with histologic features resembling those of epithelial hyperplasia, sclerosing adenosis, and microglandular adenosis, and four cases of carcinomas in fibroadenomas (CA lesions) were studied histopathologically and immunohistochemically. The CA lesions included one intraductal carcinoma, two invasive ductal carcinomas, and one lobular carcinoma in situ. The histologic features of the EP lesions and CA lesions were fundamentally the same as those of carcinomas commonly observed in the mammary gland. Immunohistochemically, smooth muscle actin was useful in the detection of myoepithelial cells, particularly in EP lesions of the adenosis type (sclerosing adenosis or microglandular adenosis), and in distinguishing carcinoma. The differences between EP lesions and CA lesions of sites of immunoreactivity to CA15-3, CEA, and EMA were also helpful for differential diagnosis.