Ductal dilation of the breast, also known as plasmacytoid mastitis and non-lactating breast abscess, accounts for about 5% of benign breast diseases. Lack of knowledge about this disease often leads to clinical errors in diagnosis and treatment. Ductal dilatation of the breast begins in women aged 30 to 40 years who have given birth and are not lactating, and there is no uniform understanding of the cause. It is generally believed to be an autoimmune disease or a degenerative disease with a cause related to endocrine disorders. It is also thought to be due to poor drainage of the ducts or other reasons that block the duct openings and retain secretions, causing duct dilation. The lesions are heavily infiltrated with plasma cells. The unique underlying lesion is a retained dilatation of the breast ducts, while the plasma cell infiltration is a secondary change and not specific to the disease. Since the disease has no specific clinical manifestations and the examination is not specific for the diagnosis of the disease, it is highly susceptible to clinical misdiagnosis and mistreatment. Because of the characteristics of breast lumps, nipple invagination, nipple overflow and axillary lymph node enlargement, this disease is often misdiagnosed as breast cancer. The authors believe that the following points can be distinguished from breast cancer: (1) Young age of onset. The age of onset of this disease is about 10 years younger than the average age of breast cancer. The average age of this group was 35 years. (2) Inflammatory manifestations such as redness, swelling, heat and pain may be present in the medical history, but the white blood cell count is not high and the classification is normal. (3) The nipple invagination can be present at an early stage and is mostly deviated. The axillary lymph nodes are enlarged with light tenderness, but they may shrink or recede as the disease progresses. (4) Most breast lumps are located around the areola and are often painful to the touch. Large thickened ducts can sometimes be palpated under the nipple or areola. The history of breast lump shrinkage and breastfeeding disorder can be found; the painless lumps of breast cancer are mostly located in the peripheral area of the breast and grow progressively. (5) Ductal mammography and needle cytology can help to differentiate. Intraoperative rapid frozen section pathological examination is a reliable basis for confirming the diagnosis and deciding on the surgical procedure. In addition, the disease is easily confused with breast tuberculosis because of the characteristics of recurrent abscesses or chronic fistulas that do not heal. However, breast tuberculosis is usually located away from the areola and the large ducts of the milk, and nipple invagination is rare. In addition, breast tuberculosis is mostly secondary and is associated with toxic symptoms and positive antibodies to tuberculosis, which helps to differentiate it. The disease is a benign breast lesion and not a precancerous lesion. Incision and drainage of abscess alone cannot achieve permanent results. In case of co-infection, the combination of methotrexate and other broad-spectrum antibiotics can achieve transient results. Surgical treatment is the only effective radical measure. For simple nipple overflow, the duct and the surrounding 0.5 cm of breast tissue are removed under the guidance of a probe; for those with subareolar masses and generally dilated large ducts under the areola, a curved incision is made at the edge of the areola, the nipple is preserved and turned, all large ducts are removed and the subareolar breast tissue is wedge-shaped. The tissue is excised, and the resulting cavity is closed with purse-string sutures, and the nipple is exfoliated with plastic sutures. (2) Segmental mastectomy: This procedure is suitable for cases with a simple breast lump that is confined to the peripheral part of the breast beyond 2.0 cm from the areola. This procedure emphasizes that the inner end of the incision must reach under the nipple to ensure complete removal of the large milk ducts to which it belongs. Otherwise, there is still a risk of subareolar cysts, nipple overflow and even mammary fistula. If there are thin strips of milk-like material overflowing from the cut surface, the excision should be expanded to prevent recurrence. (3) Simple mastectomy: Only for a few cases of diffuse lesions that have been treated unreasonably for the first time and have resulted in severe breast fistula, etc. For those who have a diffuse swelling of the breast due to combined acute infection, this is not an indication for simple mastectomy. For cases of breast fistula with controlled inflammation, complete excision of the fistula and surrounding scar tissue with preservation of the nipple and one-stage suturing is preferred. The enlarged axillary lymph nodes generally do not require special treatment and may resolve on their own after excision of the breast lesion.