Low-grade Epstein-Barr virus positive plasma cell proliferations of precursor plasma cell origin: Report of two cases

B cell lymphoproliferative disorders with plasmacytic differentiation are a spectrum of neoplasms arising from B cells in different stages of maturation, which include marginal zone lymphoma, plasmablastic lymphoma, ALK-positive diffuse large B cell lymphoma, primary effusion lymphoma, and plasma cell neoplasms. Within this group, Epstein-Barr virus (EBV) is mostly linked to plasmablastic lymphoma and primary effusion lymphoma. EBV has only rarely been associated with the remaining entities and occurs almost exclusively in immunocompromised patients. We report two cases of EBV positive, mature appearing plasma cell proliferations without previously identified immunodeficiency. The proliferating plasma cells showed co-expression of CD19, CD38, and CD138 with mono-typic surface light chain expression suggesting a plasmablastic origin. The neoplastic plasma cells were positive for EBV RNA by in situ hybridization (EBER) in both cases, and showed a low proliferation index (Ki-67 10-20%). Such lesions could be easily mistaken for plasmacytomas and low grade B cell non-Hodgkin lymphomas with extensive plasmacytic differentiation without detailed immunophenotyping and EBV studies, if the diagnosis is solely based on the morphologic features and the low proliferation index. Increased awareness of this rare or under recognized entity is necessary to better characterize this group of neoplasms and determine the best treatment approach for these patients.