Plasmablastic lymphoma of the stomach in an HIV‐negative patient

Plasmablastic lymphoma (PBL) is a rare B‐cell neoplasm with an aggressive clinical behavior that predominantly occurs in the oral cavity of human immunodeficiency virus (HIV)‐positive patients. However, it has recently been recognized that PBLs can also affect individuals without HIV infection, and suggested that these neoplasms show different clinicopathological characteristics between HIV‐positive and ‐negative patients. Herein we describe a case of gastric PBL in a female HIV‐negative patient. The tumor was composed of a diffuse and cohesive proliferation of large neoplastic cells, which resembled immunoblasts or plasmablasts with a starry sky appearance. Immunophenotypically, the neoplastic cells were diffusely positive for CD138, MUM1, IgM, and BOB‐1, and negative for CK, LCA, CD3, CD20, CD79a, Pax5, kappa, lambda, CD30, ALK, S‐100, HMB‐45, MPO, and HHV‐8. The MIB‐1 index was nearly 100%. Epstein‐Barr virus‐encoded RNA in situ hybridization was negative. A monoclonal immunoglobulin heavy chain gene rearrangement was detected in polymerase chain reaction (PCR) and heteroduplex analyses. A combination of PCR‐based analysis of immunoglobulin gene rearrangement and immunohistochemistry can be useful to substantiate the diagnosis by utilizing routine paraffin‐embedded tissue sections, because PBL in the setting of extra‐oral localization and immunocompetence is a diagnostic challenge, given its rarity, morphology, and absence of CD20 expression.