Plasmablastic Lymphoma Associated with Adjacent Mature Plasma Cell Population Exhibiting Opposite Light Chain Restriction

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.

The level of TACI gene expression in myeloma cells is associated with a signature of microenvironment dependence versus a plasmablastic signature

B-cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL) have been shown to promote multiple myeloma (MM) cell growth. We show that the main site of production for BAFF and APRIL is the bone marrow (BM) environment, and that production is mainly by monocytes and neutrophils. In addition, osteoclasts produce very high levels of APRIL, unlike BM stromal cells. Myeloma cells (MMCs) express TACI (transmembrane activator and calcium modulator and cyclophilin ligand interactor), the receptor of BAFF/APRIL, at varying levels. TACI expression is a good indicator of a BAFF-binding receptor. Expression data of purified MMCs from 65 newly diagnosed patients have been generated using Affymetrix microarrays and were analyzed by supervised clustering of groups with higher (TACIhi) versus lower (TACIlo) TACI expression levels. Patients in the TACIlo group had clinical parameters associated with bad prognosis. A set of 659 genes was differentially expressed between TACIhi and TACIlo MMCs. This set makes it possible to efficiently classify TACIhi and TACIlo MMCs in an independent cohort of 40 patients. TACIhi MMCs displayed a mature plasma cell gene signature, indicating dependence on the BM environment. In contrast, the TACIlo group had a gene signature of plasmablasts, suggesting an attenuated dependence on the BM environment. Taken together, our findings suggest using gene expression profiling to identify the group of patients who might benefit most from treatment with BAFF/APRIL inhibitors.

CD20 is associated with a small mature plasma cell morphology and t(11;14) in multiple myeloma

CD20 has been reinvestigated in 66 patients with multiple myeloma (MM). Twelve of the patients (18%) expressed CD20, including 5 of 50 patients at diagnosis presenting 100% CD20+ cells. Seven (58%) of 12 CD20+ patients with MM had a small mature plasma cell morphology as opposed to 4 (7%) of 54 with CD20- MM (P = .0001). Of note, 10 (83%) of 12 patients with CD20+ MM had t(11;14) as opposed to 5 of 54 (9%) CD20- patients (P < .001). All the patients with 100% CD20+ cells presented with t(11;14) and 4 of 5 with a small mature plasma cell morphology. Thus, 66% of the patients with t(11;14) expressed CD20, whereas only 4% of the 51 patients lacking such translocation expressed CD20 (P < .0001). In conclusion, CD20 expression is associated with small mature plasma cell morphology and with t(11;14) in patients with MM.

Phenotypic heterogeneity in aneuploid multiple myeloma indicates pre-B cell involvement

The expression of early and mature B cell markers, surface beta 2- microglobulin (B2M) and cytoplasmic immunoglobulin (clg) by aneuploid tumor cells in bone marrow aspirates from 44 patients with multiple myeloma was evaluated by correlated DNA immunofluorescence flow cytometry. Myeloma tumor cells of almost 90% of the patients contained monoclonal clg and expressed the mature plasma cell antigen R1–3 as well as surface B2M; common acute lymphoblastic leukemia antigen (CALLA) was present in 55%, B2 in 17%, and B4 in 23% of samples studied. Coexpression of CALLA and clg in 46% of all patients identified a novel myeloma phenotype without known counterpart in the normal differentiation of B cells. CALLA and clg were independently expressed and gave rise to CALLA+/clg-, CALLA+/clg+, and CALLA-/clg+ cells. The association of CALLA and mature plasma cell markers may define discrete stages of neoplastic plasma cell differentiation.

Phenotypic heterogeneity in aneuploid multiple myeloma indicates pre-B cell involvement

The expression of early and mature B cell markers, surface beta 2- microglobulin (B2M) and cytoplasmic immunoglobulin (clg) by aneuploid tumor cells in bone marrow aspirates from 44 patients with multiple myeloma was evaluated by correlated DNA immunofluorescence flow cytometry. Myeloma tumor cells of almost 90% of the patients contained monoclonal clg and expressed the mature plasma cell antigen R1–3 as well as surface B2M; common acute lymphoblastic leukemia antigen (CALLA) was present in 55%, B2 in 17%, and B4 in 23% of samples studied. Coexpression of CALLA and clg in 46% of all patients identified a novel myeloma phenotype without known counterpart in the normal differentiation of B cells. CALLA and clg were independently expressed and gave rise to CALLA+/clg-, CALLA+/clg+, and CALLA-/clg+ cells. The association of CALLA and mature plasma cell markers may define discrete stages of neoplastic plasma cell differentiation.