Relapsed multiple myeloma manifesting as extramedullary plasmacytoma of the breast: Imaging findings

Extramedullary plasmacytoma of the breast (EPB), a manifestation of multiple myeloma (MM), is very rare. It is important to recognize the imaging findings of EPB because it may be the first manifestation of relapsed MM. An 85-year-old woman presented with a lump in her right breast 4 years after the complete remission of MM. She underwent mammography and ultrasonography, which showed an oval circumscribed mass and an irregular circumscribed heterogeneous solid mass, respectively. Following ultrasound-guided vacuum-assisted breast biopsy, this lesion was confirmed to be EPB. Whole-body computed tomography showed multiple new osteolytic lesions and other multiple extramedullary lesions in addition to EPB in the right breast. The final diagnosis was relapsed MM with multiple extramedullary plasmacytoma.