Plasmablastic lymphoma of the retroperitoneum in an HIV-negative patient

Herein is reported a case of plasmablastic lymphoma (PBL) of the retroperitoneum in an HIV-negative patient. This is the first reported case of PBL at this location and of PBL from Japan in the English-language literature. A 76-year-old Japanese man was admitted to hospital with a chief complaint of right inguinal lymph node swelling. Lymph node biopsy indicated large tumor cells with both diffuse and cohesive growth patterns, and conspicuous tumor cell proliferation in lymph node sinuses. The initial pathological diagnosis was metastatic carcinoma. The patient died approximately 1 month after admission, and autopsy showed that the main lesion was a very large retroperitoneal mass. On histology diffusely proliferated plasmablast-like or immunoblast-like tumor cells were identified, which were positive on immunohistochemistry for CD138 and negative for B-cell and epithelial markers. Approximately 90% of the tumor cells were positive for Ki-67. Tumor cells were diffusely positive for EBV-encoded small RNA on in situ hybridization. The autopsy findings suggested a diagnosis of PBL. Accordingly, PBL should be considered as a differential diagnosis when lymph node biopsy findings resemble those of the present patient.