The breast is mainly composed of glands, ductal system, adipose tissue and fibrous tissue. The adult breast has 15-20 glandular lobes, each of which can be divided into many lobules, which are composed of small ducts and corresponding vesicles. The number of lobes in a breast is fixed, but the number and size of lobules can vary greatly. Each glandular lobe has its own ductal system, with multiple lobules converging to form an interlobular duct, and multiple interlobular ducts converging to form a milk duct. There are 15-20 milk ducts, arranged in a radial pattern with the nipple as the center, converging in the areola and opening in the nipple, called the milk ducts. The ducts are narrower in the nipple, then expand to form a more expanded potbelly, and later branch into various levels of ducts, with the terminal ducts connected to the alveoli. There is no anastomotic branch between the duct systems. When the cancer invades the large ducts, the large ducts become sclerotic and contracted, pulling the nipple and forming “nipple invagination”, which is one of the typical manifestations of breast cancer. The nipple and areola are elevated in the center of the breast surface, and the skin around them has obvious pigmentation and a darker color called areola. The nipple and areola contain more smooth muscle fibers, which can make the nipple erect, smaller and harder when contracted, and can squeeze the ducts to discharge the contents when breastfeeding. The skin of the areola area is rich in sebaceous glands, also known as areolar glands, which are large and superficial, nodular and elevated on the skin surface, especially during pregnancy and lactation, and have the role of protecting the skin, lubricating the nipple and the baby’s mouth and lips. The amount of adipose tissue in the breast is one of the main factors in determining the size of the breast. The entire breast, except for the areola, is surrounded by a layer of fatty tissue, and the thickness of the fatty layer varies greatly among individuals due to age, childbirth, and other factors. When the fat layer is thick, the breast feels homogeneous to palpation; when it is thin, the gland feels nodular to direct palpation. The fibrous breast tissue is wrapped throughout between the superficial and deep layers of the superficial fascia. The fibrous tissue bundles that run vertically between the lobules of the breast and are connected to each other in a network are called the suspensory ligaments of the breast, which can play a fixed role in the breast, allowing a certain degree of mobility and not significantly sagging when the breast is upright. Pathologically, if a tumor or other lesion invades the ligament, it can contract and cause skin adhesions or depressions.