[1345] Characterization of Tissue Findings in Bone Marrow with Small Monoclonal B-Cell Populations

Anmaar Abdul-Nabi, LoAnn Peterson, Beverly Nelson. Northwestern University, Chicago, IL

Background: Flow cytometry immunophenotyping (FC) allows detection of small populations of CLL type or CD5- monotypic B-cells (MBCs) in the blood. When MBCs are not associated with overt clinical disease or tissue involvement, and are <5000/uL, the term monoclonal B-lymphocytosis (MBL) is used. Most studies have focused on PB MBL, but low levels of MBCs are also found in BM. In this study, we evaluated BM pathology and clinical setting when small MBC populations similar to MBL were detected in the aspirate by flow cytometry.
Design: BMs performed between 01/1999 and 12/2010 that showed MBCs <5% of total events by 4-8 color flow cytometry were selected for review. In BM biopsies done for lymphoma staging, only small clones with a phenotype different from the original lymphoma were included PB lymphocyte counts were <5000/uL. History and physical findings were retrieved from the EMR. H&E stained BM sections and immunostains (IHC) for CD3, CD20 or PAX5 or CD79a were reviewed.
Results:

Clone Type (no. of cases)	Reason for BM				H&E/ IHC
	Lymphoma staging	AML	Plasma cell dyscrasia	Cytopenias	lymphoid aggregates (LA)	B-cell rich LA	T-cell rich LA
CLL (11/24)	6	2	1	2	5/11	3	2
None CLL (13/24)	6	0	4	3	4/13	1	3

The majority of cases with either CLL or non-CLL type B-cell clones did not exhibit lymphoid infiltrates in the BM biopies. The cases that did have LA's were not considered diagnostic for lymphoma; all represented <5% of cellularity and were non- paratrabecular; 5 were T cell rich and 4 B cell rich and were insufficient to established lymphoma.
Conclusions: In this study, small MBC clones were found in BM and were of both CLL type and non-CLL (CD5-) but the CD5- phenotype predominated, in contrast to those reported in the blood. Most BM biopsies with either type MBC had no lymphoid aggregates or no overt morphologic or IHC evidence for lymphoma. Recognition of these small B cell clones are important in evaluating BM biopsies for lymphoma as their presence, similar to PB, may not be equivalent to lymphoma.
Category: Hematopathology

Monday, March 19, 2012 1:00 PM

Poster Session II # 206, Monday Afternoon