Preneoplasia of the breast.

The present review emphasizes the pathology of premalignant ductal breast diseases, based on a three-cell concept of the breast. Immunohistochemical analyses using smooth-muscle actin, keratin 5/6, keratin 8/18/19 and MiB-1 proliferation antibodies demonstrated three different cell types in the normal breast: k 5/6 positive committed progenitor cells, k 8/18/19 positive glandular cells and smooth-muscle actin-positive myoepithelial cells. All hyperplastic lesions were shown to contain a mixture of those cells. According to their components, the hyperplastic lesions were subdivided into epithelial-myoepithelial, purely epithelial and myoepithelial lesions. All usual epithelial hyperplasias (= ductal hyperplasias) were composed of committed progenitor cells and glandular cells. On the contrary, ductal carcinoma in situ showed a monotonous cell pattern which, in the majority of cases, express k 8/18/19 and, in a minority (10-15%), k 5/6, signifying an unidirectional differentiation.