Plasma cell mastitis is a chronic non-bacterial inflammatory disease of the breast. Due to the complex and variable pathological features, there are various names, such as “occlusive mastitis”, “chronic mastitis”, “ductal dilatation of the breast”, “acneiform mastitis”, etc. acne-like mastitis”, etc. Plasmacytoid mastitis occurs in middle-aged and older women, with a peak age of 50 to 60 years, and most patients have nipple invagination. The cause of plasmacytoid mastitis, a benign lesion, is still unclear. It is due to irregular epithelial hyperplasia of the mammary glands, malfunction of secretion, and the accumulation of large amounts of lipid-laden secretions in the milk ducts under the nipples and areola, resulting in dilation of the milk ducts, followed by decomposition of the accumulation in the milk ducts. Fibrous tissue proliferation. At this point, if the lesion expands further, an inflammatory mass can be formed. Sometimes the inflammation is acute and becomes an abscess, and the pus is often mixed with slag-like material, and there is also slag-like material discharged from the nipple orifice, which is called “pimple-like mastitis”. The most important thing is to have a good understanding of the situation. The clinical manifestations of plasmacytic mastitis Plasmacytic mastitis has a sudden onset and develops rapidly. The patient feels localized pain and discomfort in the breast, and a lump may be palpable. The lump is located under the areola or extends into one quadrant. The masses are hard and tough. The surface is nodular, with poorly defined borders and no adhesions to the chest wall. The skin of some breasts is edematous and orange peel-like, and there are usually no systemic symptoms such as fever. The nipples are often edematous and orange peel-like, usually without fever and other systemic symptoms. The nipples often secrete powder-like material with a foul odor. A small number of patients have nipple discharge, which is bloody or watery, and may be accompanied by enlargement of the axillary lymph nodes on the affected side. In the late stage, the lump becomes softened and forms an abscess. The abscess breaks down and flows pus mixed with powder-like pus and causes fistulas in the areola, resulting in recurrent wounds and scarring, which causes the nipple to sink into a concave position. The clinical manifestations of plasmacytoid mastitis are varied, with some patients exhibiting prolonged nipple discharge, or nipple invagination alone, or localized lumps that persist for years. Treatment of plasmacytoid mastitis Treatment depends on the clinical presentation, but the main point of treatment is to surgically remove the diseased ducts in order to achieve a complete cure. The lump may be excised in the case of a limited mass, an incision may be made to drain the abscess, or a fistula may be removed in the case of a fistula. In some cases, mastectomy may be considered for most chronic fistulas or severe breast deformities that are too long in duration. Plasmacytoid mastitis can be easily confused with non-lactating septic mastitis, breast tuberculosis, and especially with fistulas formed when the tuberculosis breaks down. When there is nipple invagination combined with a lump, it can be easily confused with breast cancer, so sometimes a local biopsy is needed to identify the difference.