CD3-positive plasmablastic lymphoma reported in two cases: A potential diagnostic caveat

Plasmablastic lymphoma (PBL) is a rare aggressive subtype of mature large B cell lymphoma involving almost exclusively the extranodal regions particularly the oral cavity, frequently described in immunocompromised patients. PBL is characterized histologically by diffuse proliferation of large neoplastic cells resembling B immunoblasts or plasmablasts. The diagnosis of PBL can be difficult due to its ambiguous histopathological features mimicking most large cell lymphomas and lacking a distinctive immunophenotypic pattern. They typically lack expression of CD20 and CD79a but may express plasma cell marker, CD138. Aberrant immunoexpression of CD3, a T-cell marker in PBL in the absence of other B-cell markers is exceptionally rare, may potentially lead to incorrect interpretation. Herein, we report a case series of CD3-positive PBL of oral cavity in two individuals, which were initially misdiagnosed as high-grade T-cell lymphomas including extranodal NK/T-cell lymphoma, nasal type. Useful distinguishing clinical settings, histomorphological features, immunohistochemistry and molecular expression profiles of PBL are discussed.