The human embryo develops 6-8 pairs of primordial mammary primordia along the anterior wall of the trunk from the axilla to the inguinal line (mammary line) at week 6. The primordial pair of mammary glands in front of the chest gradually develops into normal mammary glands during adolescence (around 11-15 years old), while the rest of the primordial glands do not develop and gradually degenerate and disappear. Third, due to various factors, mainly the absolute or relative increase in estrogen levels, the undeveloped primordial glands of women redevelop, and a structure similar to a mammary gland appears on the breast line, which is called a paramammary gland because it is not a formal mammary gland. Most paramammary glands have only glandular tissue and no nipples, ducts, or other milk transport structures. Paramammary glands can occur at any age after puberty, but are more common during pregnancy and lactation. Parammary glands can appear anywhere on the breast line or even in other locations of the body, but most of them appear in the armpit. The incidence of parametrial cancer is very low, accounting for only about 0.2% of breast cancer, that is to say, for every 1000 breast cancer patients in the population, only 2 or 3 patients with parametrial cancer will appear. In our breast center, there are more than 600 cases of breast cancer each year, but only 2 cases of parametrial cancer in the past two years, so it is totally unnecessary for many women to worry about parametrial cancer. There is no special medication for parametrial gland, and most of them do not need surgery unless they are large and affect daily life or patients feel that they are an eyesore. Some patients often feel significant pain in the location of the parametrial gland under the armpit and expect to have the parametrial gland removed surgically to relieve the pain, but many patients cannot achieve their goal. The parammary gland is very common in women and usually there is no need to care about it. However, if you find a lump in the parametrial area, you should go to a regular hospital in time. The annual routine physical examination of the breast will also include the parametrial gland.