Plate 3 illustrates the normal and abnormal whole mount morphology of the mouse mammary gland (Figures 3A and 3B) and the morphologic progression in the human mammary gland that is believed to lead to breast cancer (Figures 3C to 3H).

A. (Figure l.) Whole mount of portion of mammary gland number four, C3H mouse, 6 weeks old. Note duct system with end buds but no alveoli.

B. (Figure 2.) Whole mount of a portion of the mammary gland of a parous, nonpregant C3H mouse. Note four hyperplastic alveolar nodules (HAN). Parous mammary gland has scattered alveoli not present in the gland of the virgin animal.

C. (Figure 19.) Subgross preparation of mammary gland of a 52 year old woman with irregular menses. Note small lobules and cysts resulting from obstruction of extralobular terminal ducts (by inflammation), causing distension of the lobules with secretion. The lobules "unfold", eventually producing single isolated distended cysts.

D. (Figure 20. Subgross preparation of mammary gland of a woman in her 4th decade showing two atypical lobules, type A, (ALA) in the mid-lower center of the illustration. The surrounding tissue has well developed lobules, a duct (convoluted structure, cross section, lower right) and a dilated lobular formation of uncertain type (upper right). The ALA consist of greatly enlarged lobules with enlarged acini lined by thickened epithelium with visible intraluminal papillary projections and cribriform pattern. Cytological atypia which might be present in ALAs is not predictable from examination of the subgross preparation. Bright field microscopy of stained histology slides is required. The ALA's shown here might have been diagnosed as "blunt duct adenosis", a term now seldom used.

E. (Figure 21.) Histology slide stained with H and E reveals three different degrees of cytological atypia within adjacent portions of an ALA similar to the larger one in figure 20. The enlarged acinus to lower right has low grade atypia featuring a relatively simple epithelial lining of uniform thickness with cuboidal and low columnar luminal cells overlying myoepithelial cells (small dense bean-shaped nuclei) and presumed germinal cells (larger pale nuclei). The acinus to the left has a diffuse formation of epithelial cells which partially fill the lumen and form a more solid zone centrally, an appearance often seen in intermediate grade atypia. The acinus at upper right has well developed cribriform (micropapillary) pattern characteristic of high grade atypia, bordering on carcinoma-in-situ.