The breasts are located on both sides of the chest, between the level of the second and sixth ribs, and are mostly hemispherical with the nipple in the center and the dark colored part around the nipple called the areola. The breast gland consists of about 15 to 20 lobes, which are arranged in a radial pattern with the nipple as the center. Each lobe is divided into several glandular lobules, each of which is composed of 10 to 100 glandular vesicles. These vesicles are arranged closely around the small milk ducts, and the openings of the vesicles are connected to the small milk ducts. The ducts converge to form interlobular ducts, which further converge to form a duct for the entire lobe, also known as the milk duct. There are 15 to 20 milk ducts, which are arranged in a radial pattern with the nipple as the center, converging on the areola and opening at the nipple, called the milk ducts. The milk ducts are narrower at the nipple and then expand into a pot belly called the sinus of the milk duct, which has the role of storing milk. The opening of the ducts is lined with squamous epithelium, the narrowing is lined with migrating epithelium, and the ducts below the pot belly are lined with double-layered columnar epithelium or single-layered columnar epithelium, and the terminal ducts are lined with cuboidal epithelium near the alveoli. There is also a narrow part of the breast tissue protruding into the axilla, which is the caudal part of the breast. Except for the areola, the entire breast tissue is surrounded by a layer of fat, and the size of the breast is related to the thickness of the fat layer. The fat capsule contains bundles of connective tissue fibers that run in different directions, called Kubert’s ligament. It is attached by the base of the gland to the skin or the superficial fascia of the chest and the pectoralis fascia, forming walls and pillars that separate the lobes of the breast and provide a certain degree of fixation to the position of the breast. In breast cancer patients, its fibrous bundle shortens and pulls the skin inward, causing the local skin to show orange peel-like changes. The interlobular stroma is loose mucus-like or reticular connective tissue that varies with the functional state of the ovaries, so it can be considered part of the lobular parenchyma, but is clearly delineated from the peripheral interlobular connective tissue. The interlobulars are dense connective tissue, which is not subject to endocrine influence. Intralobular connective tissue is physiologically and pathologically important, and intraductal fibroatheromas are the result of such connective tissue hyperplasia. Most fibrosarcomas of the breast are also the result of lesions in this layer, and all hyperplastic diseases of the breast tissue are associated with hyperplasia in this layer.