Plasmablastic lymphoma of the cecum: report of a case with cytologic findings.

Plasmablastic lymphoma (PBL) is a rare lymphoma that is characterized by a diffuse proliferation of large neoplastic cells resembling B immunoblasts, but shows the immunophenotype of plasma cells. PBL is most commonly seen in the oral cavity of human immunodeficiency virus (HIV)-positive patients. Epstein-Barr virus (EBV) may be closely related the pathogenesis of PBL. We report a case of HIV-negative PBL in a 75-year-old man without EBV infection. Histologic examination of the cecal tumor following right hemicolectomy and cytologic examination of ascitic fluid were performed. Cytologic specimens were hypercellular and composed of single cells and loosely formed clusters. Large tumor cells showed plasmacytoid features with basophilic cytoplasm, large nuclei, prominent nucleoli, and focal perinuclear halos. Abnormal mitotic figures were easily identified. On immunohistologic study, the tumor cells were positive for CD138 (plasma cell marker) and kappa, but negative for CD45, CD3, CD20, CD79a, CD56, and cyclin D1. The proliferation index (Ki-67) was high. This is a very rare case of PBL without HIV and EBV infection, involving the cecum.