Plasmablastic Myeloma versus Plasmablastic Lymphoma: Different Yet Related Diseases

Plasmablastic myeloma (PBM) is a rare, monoclonal, immunoproliferative plasma cell neoplasm that shares many characteristics with plasmablastic lymphoma (PBL) [1]. Currently, there are no set standards for differentiating between PBL and PBM. Morphologically, PBM is characterized by the presence of large plasma cells with large hyperchromatic nuclei, one or more prominent centrally-located nucleoli, a rim of basophilic cytoplasm, high nuclear/cytoplasmic ratio, and an increased number of mitoses [2]. Plasmablastic myeloma is more likely to express CD38 and CD138 with light chain restriction [3]. Yet, in a small study of 16 patients (9 cases of PBL and 7cases of PBM), all cases had immunochemistries positive for MUM1/IRF4, CD138, and CD38, and negative for CD20 [1]. Indicating that simply using CD38 and CD138 positivity to differentiate between PBL and PBM is unreliable (Table 1). Moreover, another study concluded that a patient with PBM was positive for CD38 and MUM-1, but negative for CD138 [2]. Thus, there are conflicting reports for the ability of immunohistochemical studies to differentiate between PBL and PBM.