Ductal epithelial hyperplasia of the breast, a pathological type of cystic hyperplasia of the breast. Cystic hyperplasia of the breast is a common and frequent disease in women and is named differently depending on the understanding of the disease. The pathological pattern is diverse, and hyperplasia can occur in the ductal epithelium, periductal tissue, and within the lobules of the breast. If it occurs in the ductal epithelium, it can be characterized by various degrees of papillary hyperplasia with cystic dilatation of the milk ducts; if it occurs in the parenchyma of the breast lobules, it is mainly characterized by hyperplasia of the milk ducts and alveolar epithelium; if it occurs in the peri-glandular ducts, it can be accompanied by the formation of cysts of various sizes containing yellowish or brownish fluid.