Case Description:
A 59-year-old HIV-negative man presented with abdominal pain. The CT scan found extensive retroperitoneal lymphadenopathy including a large pelvic mass. A core biopsy showed relatively cohesive sheets of large, atypical cells with round/oval to irregular pale nuclei, multiple nucleoli, and abundant amphophilic cytoplasm (A, x400). Mitotic figures, apoptosis, and focal necrosis were present. Immunostaining showed the cells were positive for CD3 (cytoplasmic, B, x400), CD4 (C, x400), CD138 (D, x400), MUM1 (E, x400), MYC (F, x400), OCT2, and Kappa light chain (G, x400). CD79a and PAX5 (H, x400) were weakly positive in a subset of cells. CD2, CD5, CD7, CD8, CD10, CD20, CD30, CD45, CD56, AE1/AE3, S100, ALK1, and HHV8 were not expressed. EBV (I, x400) was diffusely positive. FISH was positive for MYC rearrangement. Analysis of IG H/K and TR G/B rearrangements showed IG rearrangement. Bone marrow was not involved. These results support the diagnosis of plasmablastic lymphoma (PBL). PBL is a rare neoplasm with a plasmablastic morphology and immunophenotype and may aberrantly express T cell-associated markers. Expression of both CD3 and CD4 is exceedingly rare.(1, 2) As common B-cell immunomarkers are usually negative in PBL, expression of T-cell markers may lead to misclassification of this lymphoma as a T cell or NK cell lymphomas.