The extramedullary plasmacytoma (EMP) is a malignant tumor primarily formed by the monoclonal proliferation of plasma cells outside the marrow hematopoietic tissue. Extramedullary plasmacytoma of the breast is rare, especially primary extramedullary plasmacytoma of the breast. This paper reports a case of 22-year-old female whose wound of left-breast mass excision ulcerated repeatedly for 4 years and the patient was diagnosed as the primary extramedullary plasmacytoma of the breast. The PET/CT examination suspected the left axillary lymph node metastasis. The patient’s condition improved significantly after the radiotherapy and chemotherapy.