Two Cases of Plasmablastic Myeloma Mimicking Plasmablastic Lymphoma With In-Depth Review of Literature

Plasmablastic myeloma (PBM) is a rare, aggressive subtype of multiple myeloma (MM) with poor prognosis. On the other hand, plasmablastic lymphoma (PBL) is an aggressive B-cell lymphoma with a plasmacytic phenotype. Importantly, PBM is difficult to distinguish from PBL, because clinical features of both diseases closely overlap. We report two cases of PBM accompanied by apparent extramedullary lesions.

Case 1: A 38-year-old female complained of fatigue. She presented with pancytopenia, splenomegaly, a soft tissue lesion over the chest wall, and multiple osteolytic lesions. Initially, pathology of the soft tissue established a diagnosis of PBL. She received two cycles of EPOCH, leading to considerable improvement. She then received daratumumab (Dara) and lenalidomide, achieving remission for two years. Case 2: A 60-year-old male was evaluated for multiple tumors of the pancreas and retroperitoneum. A biopsy of the pancreatic tumor identified plasmacytoid cells, whereas a biopsy of the bone marrow showed no evidence of plasma cells. Therefore, he was initially diagnosed as having multiple plasmacytomas and received 3 cycles of chemotherapy with bortezomib (Bor), lenalidomide, and dexamethasone, but in vain. Once Bor was replaced to Dara, he rapidly developed panperitonitis and ascites filled with plasmablasts and eventually died of multiple organ failure.

As there is no standard treatment for PBM, our cases raise a possibility that combination therapy with anti-myeloma and anti-lymphoma regimens may provide better outcomes. In addition, the Ki-67 proliferation index would be a useful tool to diagnose PBM.