MM-230: Solitary Extramedullary Plasmocytoma Mimicking a Primary Breast Cancer

Abstract

Extramedullary plasmocytoma is a plasma cell neoplasm that arises outside the bone marrow in the absence of any other sign of multiple myeloma. Breast plasmocytoma has been reported as part of disseminated disease. However, primary solitary breast plasmocytoma is rarely described. Here, we present a case of solitary extramedullary breast plasmocytoma mimicking a primary breast tumor. A 50-year-old female patient presented to our clinic for a left breast lump of one month duration without any associated systemic symptoms. Mammography and breast ultrasound showed a suspicious, well-defined, 2-cm mass in the left upper quadrant without ipsilateral lymphadenopathies. Tru-cut biopsy from the breast lesion revealed unexpectedly atypical monoclonal plasma cells (kappa monoclonality). Serum protein electrophoresis and immunofixation of serum protein, as well as urine protein electrophoresis and Bence Jones proteins, were negative for any M-protein/monoclonal gammopathy. Bone marrow aspirate and biopsy disclosed less than 3% clonal plasma cells. 18F-FGD PET-CT did not show any lytic lesions nor other pathologic findings. These results supported the diagnosis of solitary extramedullary plasmocytoma of the breast. Subsequently, our patient was referred for wide local excision of the solitary lesion. She received a consolidative radiation therapy post-operatively. Fifteen months later, the patient is on regular follow-up without detection of any monoclonal gammopathy. Usually, extramedullary plasmocytoma occurs in the head and neck. Few cases are reported in the breast. Clinicians should be aware of this entity, mimicking primary breast cancer. It does not have specific clinical or radiological features. The diagnosis requires: extramedullary tumor with evidence of clonal plasma cells, normal skeletal survey, no M-protein in serum and/or urine, and no bone marrow involvement. Soft tissue extramedullary plasmocytomas have better prognosis than plasmocytomas occurring in bone. The treatment of choice is radiation therapy with curative intent and low risk of recurrence after tumoricidal radiation.