Peripheral T cell lymphoma of the nasopharynx with expansion of EBV-positive B cells masquerading as an extranodal NK/T cell lymphoma, nasal type.

Epstein-Barr virus-infected B cells are found at high frequency in peripheral T cell lymphoma. Herein, we report a case involving excessive EBV-positive B cells accompanying peripheral T cell lymphoma, not otherwise specified in the nasopharynx masquerading as nasopharyngeal extranodal NK/T cell lymphoma. A large number of Epstein-Barr virus-infected B cells infiltrate in between CD3-positive cytotoxic tumor T cells, as if EBV was infecting tumor T cells. After chemotherapy, the T cell lymphoma population decreased, but the B cell population expanded to form EBV-positive diffuse large B cell lymphoma in the tonsils and nasopharynx. At the follow-up, bone marrow biopsy exhibited infiltration of composite peripheral T cell lymphoma, not otherwise specified, and EBV-positive diffuse large B cell lymphoma. Although this condition is rare, the cell lineage of EBV-infected cells must be confirmed when diagnosing extranodal NK/T cell lymphoma to exclude the possibility of misdiagnosis by Epstein-Barr virus-infected B cells.