Extramedullary plasmacytoma (EMP) occurs as a result of abnormal proliferation of plasma cells outside the bone marrow. Breast plasmacytomas are rare. Radiologically, they can be confused with benign and malignant lesions of the breast. It is important to be able to diagnose EMP in the breast since the treatment strategy is different from that of other lesions and allows for the diagnosis and early treatment of multiple myeloma (MM) relapse. We report imaging and clinicopathological findings of an EMP case in which a 65-year-old patient with MM in remission presented with breast masses.