Plasmablastic Lymphoma : CD138

CLINICAL: Plasmablastic lymphoma is a variant of diffuse large B-cell lymphoma (DLBCL) seen mainly in immunodeficient patients [HIV (most common), organ transplant recipients, autoimmune diseases]. Occasional cases occur in immunocompetent individuals. The most common location is the oral cavity. There is striking male predominance and the median age is 4th and 5th decades of life. The prognosis is poor; majority of the patients die within one year of diagnosis. MORPHOLOGY: The tumor is composed of diffuse sheets of plasmablasts with a starry sky pattern. The tumor cells are large with eccentric nuclei, single central prominent nucleolus, and abundant basophilic cytoplasm. Mitotic activity and apoptosis are prominent. The differential diagnosis includes anaplastic plasmacytoma, Burkitt lymphoma, and DLBCL, NOS. IMMUNOPHENOTYPE: The immunophenotypic profile is similar to plasma cells : negative for CD45 with low/absent pan B-cell markers (CD20, CD79a, and PAX5) and positive for plasma cell-associated markers (CD38, CD138, IRF4/MUM-1 and VS38c), with variable expression of immunoglobulins. BCL6 is negative or only focally positive. Ki67 proliferation index is high. EBV is positive in 75% of cases. HHV8 is negative. References: 1) Jaffe, ES et al. (2011), Hematopathology, Saunders/Elsevier, Philadelphia, PA. 2) Colomo et al. Diffuse large B-cell lymphomas with plasmablastic differentiation represent a heterogenous group of disease entities. Am J Surg Pathol 2004;28:736-747.