Reactive Intra-sinusoidal Immunoblastic Proliferations in Lymph Nodes: A Diagnostic Pitfall for Diffuse Large B-Cell Lymphoma

Document Type

Conference Proceeding

Publication Date

3-1-2024

Publication Title

Lab Invest

Abstract

Background: Reactive intra-sinusoidal immunoblastic proliferations (ISIPs) in lymph nodes (LNs) can mimic sinusoidal Diffuse Large B-Cell Lymphoma (DLBCL). ISIPs are not rare but poorly characterized and are a major pitfall for the misdiagnosis of lymphoma. Design: We characterize the clinicopathologic features of 12 patients with ISIPs in LNs. Results: The cohort included six men and six women with a median age of 46 years (range: 4-71). Nine had no lymphadenopathy and biopsies for tumor resection, sore throat, intestinal obstruction, and intussusception. The collection included a tonsil, five mesenteric, and three axillary LNs. Three patients presented with axillary lymphadenopathy and a suspected lymphoma. All cases showed sinuses expanded by immunoblasts, intermediate to large-sized lymphoid cells with round to slightly irregular nuclei, vesicular chromatin, and distinct, often single nucleoli with moderate amounts of cytoplasm. Scattered small lymphocytes also presented as a minor component. Otherwise, reactive secondary follicles were present in the LNs. In all 12 cases, most immunoblasts were of B-cell lineage, CD30, CD38, CD43, CD45, CD79a, and MUM1/IRF4 were positive. In ten evaluated cases, CD20 was uniformly positive in three (30%), partially positive in five (50%), and negative in two (20%). PAX5 was weak to partial in five (56%), negative in four (44%), and not assessed in three cases. In four cases, there were small subsets of T-cell immunoblasts expressing T-cell markers: CD2, CD3, and CD5. The immunoblasts in all cases were negative for CD10, CD15, BCL2, BCL6, CD138, and ALK1. In eight of 12 cases tested, the B immunoblasts were polytypic by light chain evaluation. In 10 of 12 cases tested, EBER was negative. The Ki-67 proliferation index was high (range: 60-90%). In eight of 12 cases tested, IGH rearrangement studies were negative for clonality. A representative case is shown in Figure 1. Conclusions: Reactive ISIPs in LNs are predominantly of B-cell lineage with a post-germinal center immunophenotype and a high proliferation rate. Given the large cell morphology of immunoblasts, it is critical to distinguish these lesions from sinusoidal DLBCL involving LNs. While the lymphoma cells of a sinusoidal DLBCL often express CD30, they are uniformly positive for B-markers, including CD20 and PAX5, and carry clonal IGH rearrangements.

Volume

104

Issue

3

First Page

S1462

Last Page

S1463

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