CD3⁺ CD56⁺ EBER1⁺ atypical extraosseous plasmacytoma of the nasal cavity

We present a case of atypical extraosseous plasmacytoma (EP) with a plasmablastic morphology and CD3⁺ CD56⁺ Epstein–Barr virus-encoded RNA-1 (EBER1)⁺ phenotypes of the nasal cavity. A 51-year-old male attended a local hospital with a tumor located in his left nasal cavity that was histologically diagnosed as extranodal NK/T cell lymphoma, nasal type. We reviewed the specimens and re-biopsied the tumor, and confirmed that the tumor was positive for CD3, CD56, and EBER1; however, the tumor showed a plasmablastic morphology without necrosis and angiocentricity, and was positive for CD138, but negative for CD20 and PAX5. Given a plasmablastic morphology and EBER1 positivity, but a relatively low Ki67 index (30%), we diagnosed the case as atypical EP. The CHOP regimen was administered and complete remission achieved. This case indicated that EP should be considered as a differential diagnosis even when a tumor shows large cell morphology and is positive for CD3, CD56, and EBER1.