Plasmacytoid mastitis Plasmacytoid mastitis is a relatively uncommon aseptic benign breast lesion characterized by marked dilatation of collecting ducts at the areola, periductal fibrosis and massive inflammatory cell, especially plasma cell, infiltration, also known as ductal dilatation and periductal mastitis. The etiology of this disease is not well understood, and it is generally believed that the early stage may be an anaerobic bacterial infection for which common antibiotic therapy is ineffective. The other is thought to be an autoimmune disease. The onset of the disease is characterized by a young age of onset, mostly in non-pregnant lactating women aged 30-40 years. The majority of patients have non-cyclic breast pain, with redness, swelling, heat and pain in the acute phase, accompanied by enlarged ipsilateral axillary lymph nodes, which can be easily misdiagnosed as acute mastitis, and may be accompanied by nipple discharge, mostly watery plasma or purulent, and may have bloody discharge. The affected breast often has nipple invagination or deformation. The duration of the disease varies, and can last for several months or years. A mammogram shows a uniform dense mass in the subareolar area. Treatment: For the acute inflammatory phase, the first treatment is with anti-anaerobic drugs, and for those who still have breast masses after the acute inflammation has improved, they are treated with triamcinolone acetonide (tamoxifen). Surgical excision of the lesion site is feasible locally, in a zone or quadrant. Large masses, diffuse lesions, and sinus tract formation may be treated with simple mastectomy.