Multiple myeloma presenting with multifocal Epstein-Barr virus-encoded RNA-positive plasmacytomas: A case report

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Epstein-Barr virus-encoded RNA (EBER) positivity is uncommon in multiple myeloma and may raise diagnostic concern for plasmablastic lymphoma (PBL), particularly when tumor-forming lesions predominate. A 62-year-old woman without an overt immunosuppressive condition presented with a progressively enlarging mass around the right humerus after a traumatic fracture. Imaging demonstrated multifocal osteolytic lesions with soft tissue masses, and biopsy of the right humeral lesion revealed a CD138-positive, kappa-restricted plasma cell neoplasm with EBER positivity. Bone marrow examination showed only 1% morphologically abnormal plasma cells; however, marked IgG-kappa monoclonal gammopathy, Bence Jones kappa proteinuria, anemia, multifocal osteolytic bone lesions, and a biopsy-proven plasmacytoma supported a diagnosis of IgG-kappa multiple myeloma with Bence Jones kappa proteinuria, presenting with multifocal EBER-positive plasmacytomas. The patient received proteasome inhibitor-, immunomodulatory drug-, and anti-CD38 antibody-based therapies, radiotherapy, and delayed autologous hematopoietic cell transplantation after additional stem cell mobilization with granulocyte colony-stimulating factor plus plerixafor. She achieved a stringent complete response and has maintained it for more than six years without maintenance therapy. This case highlights the diagnostic difficulty of EBER-positive plasmacytoma-­dominant myeloma and the importance of integrated clinicopathological assessment to distinguish it from PBL.