Histopathological EXAMINATION of BONE MARROW Biopsy (BMB) IN Primary Splenic B CELL Lymphomas of Marginal-ZONE ORIGIN (PSMZL). A Reliable Substitute for Spleen Pathology?.

Abstract 1924

Poster Board I-947

According to the 2008 WHO Classification, PSMZLs mainly comprise splenic marginal-zone lymphoma (SMZL) and splenic diffuse B cell lymphoma/leukemia unclassifiable (SDLU). Until recently, histological examination of splenectomy specimens was considered as a prerequisite for the diagnosis of SMZL though, due to the recent advancement in chemo-immunotherapy therapies, splenectomy is no longer performed in most cases. We evaluated the diagnostic efficiency of BMB examination in the documentation of the diagnosis of PSMZLs and their differential diagnosis from mimickers, including other small B-cell lymphomas, and tested whether BMB may serve as a substitute for spleen microscopic examination in the differential diagnosis of SMZL from SDLU. The study group included 108 BMB samples from patients with a diagnosis of PSMZL based either on examination of splenectomy specimens (n= 46), or clinical presentation, cell morphology and flow cytometry analysis (n= 62). Histological and immunohistochemical results are summarized in Table 1. Molecular analysis of immunoglobulin genes showed that 10/21 analyzed CD27+ cases carried IGHV genes with more than 98% germline identity (unmutated), whereas 5/8 analyzed CD27- cases carried mutated IGHV genes. Furthermore, 7/14 analyzed SIgD+ cases carried mutated IGHV genes. Splenectomy specimens were available in 46/108 cases. Blinded histopathological examination of the spleens revealed 35 SMZL and 11 SDLU. Paired assessment of BMB and spleen specimens did not identify any discriminating pattern of BM infiltration and/or morphology between SMZL and SDLU; notably, the immunophenotypical profile of BMB and spleen specimens was identical when 14 different markers have been utilized (Table 1). In conclusion, our study documents the value of BMB histopathology in the diagnosis of PSMZLs and their differential diagnosis from other small B-cell lymphomas primarily or secondarily involving the spleen. Presently, it is not possible to distinguish SMZL from SDLU based on the only BMB histopathology. Finally, our results confirm and expand the considerable heterogeneity of PSMZL, which could reflect different activation status and/or different histogenesis of the clonogenic cells.