Figure 1.

Cartoon drawing depicting the spectrum of intraductal proliferations of the breast. The normal milk duct demonstrates a single layer of normal luminal epithelial cells, bound by an intact myoepithelial cell and basement membrane layer. In the case of (usual) ductal hyperplasia, there is epithelial cell proliferation, but these cells retain normal morphology. Atypical (ductal) hyperplasia (ADH) demonstrates both epithelial cell proliferation and low-grade, monomorphic cytological atypia, but the involvement of the duct is generally limited. DCIS may include either more extensive low-grade atypical cells (similar in morphology to ADH) or an intraductal proliferation with greater cytological atypia but an intact basement membrane. Finally, invasive ductal carcinoma includes cytologically atypical cells with a disrupted myoepithelial cellular layer and basement membrane, which allows invasion of the carcinoma cells into the surrounding stroma.