Faculty Bibliography

Plasmablastic lymphoma (PBL) is an aggressive high-grade B cell lymphoma, considered a variant of diffuse large B cell lymphoma with approximately 75% mortality within 6-7 months. We describe an unusual case of PBL arising as a maxillary mass in an HIV-negative, nontransplanted 78-year-old female. Histologic examination revealed a diffuse infiltrate of anaplastic appearing cells exhibiting plasmablastic morphology with an adjacent contiguous infiltrate of mature appearing plasma cells. The PBL and mature plasma cell components both demonstrated an immunophenotype of CD20(-), CD38(+), and CD138(+). The two populations differed by the PBL featuring a high proliferation rate by Ki-67 (~95%) with coexpression of both c-MYC and EBV, while the mature plasma cell component featured a low proliferation rate by Ki-67 (~5%) without coexpression of c-MYC or EBV. Kappa/lambda staining demonstrated lambda light chain restriction involving the PBL, while the mature plasma cell infiltrate revealed kappa light chain restriction. Our findings describe the rare association of PBL with a synchronous distinct population of mature plasma cells exhibiting opposite light chain restriction.

Anterior mediastinal biopsies consisting predominantly of small lymphocytes can be a diagnostic challenge, especially in small core biopsies. In these cases, immunophenotyping is often employed using flow cytometry, and/or immunohistochemistry. However, due the overlap in T-cell phenotype between thymic neoplasm/hyperplasia (THY), T-lymphoblastic lymphoma (T-LBL), and reactive lymph nodes (RLN), biopsies consisting predominantly of T-cells may still be difficult to differentiate. Previous studies have shown a specific CD3/bcl-2 staining pattern in thymic T cells of humans and mice using flow cytometry. However, the utility of this finding in distinguishing T-cells of THY, T-LBL, and RLN has not been carefully evaluated. Our findings show that the pattern of CD3/bcl-2 expression in thymic T-cells can be used to help diagnose anterior mediastinal biopsies, even when limited specimen is provided. © 2017 International Clinical Cytometry Society.