Features of plasmablastic lymphoma in an HIV-positive patient:
(1) The clinical course is aggressive and can be rapidly fatal.
(2) Tumors are typically extramedullary and extranodal at presentation. Sites may include oral cavity, bone, soft tissue, the GI tract, spermatic cord, the sinonasal cavity and/or orbit.
(3) The extent of the tumor can be appreciated on PET scanning.
(4) Microscopic examination shows diffuse proliferation of large cells with atypical plasmacytoid features.
(5) Tumor cells are CD138, CD38 and MUM1 positive but CD20, bcl-6 and PAX5 negative.
(6) Mitotic figures are common and the proliferative fraction is high (Ki67 index > 90%).
All tumors are positive for Epstein-Barr virus (EBV). The virus can be demonstrated on in situ hybridization (ISH).
Many tumors are positive for HHV-8 by PCR but its latent nuclear antigen (LNA) is absent, indicating infection of nonneoplastic bystander cells.
Differential diagnosis:
(1) multiple myeloma
(2) plasmablastic transformation of myeloma
(3) plasmablastic lymphoma associated with Casteleman’s disease (plasmablasts are CD20-positive and are IgM lambda restricted)
(4) immunoblastic lymphoma
(5) Burkitt’s lymphoma with plasmacytoid differentiation
(6) ALK-1 positive large B-cell lymphoma
(7) primary effusion lymphoma
