Abstract and Introduction
Abstract
Objectives: Bone marrows (BMs) with incidentally identified, small monotypic B-cell populations (MBPs) were evaluated.
Methods: BM aspirates with MBPs representing 5% or less of total events by flow cytometry, less than 5.0 × 10/L B cells in blood, and no history of lymphoma or MBP with a different phenotype from prior lymphoma were selected. Clinical, immunophenotypic, and histologic findings were evaluated.
Results: Forty-one of 3,052 BMs had MBPs at 5% or less of total events (median, 1%); 17 were females and 24 were males aged 30 to 87 years (median, 73 years). The MBPs were CD5− in 24, CD5+ resembling chronic lymphocytic leukemia (CLL) in 13, and CD5+ unlike CLL in four. Eighteen of 40 had lymphoid aggregates (LAs) with mostly T cells or a mixture of B and T cells, but three cases had B-cell–rich LAs.
Conclusions: Unlike monoclonal B lymphocytosis in blood, MBPs in BMs were more commonly CD5−. Forty-five percent of BMs had LAs; none were interpreted as lymphoma, although three were suspicious for B-cell lymphoma.
Introduction
Monoclonal B lymphocytosis (MBL) is defined as the presence of less than 5.0 × 10/L monoclonal B cells in the blood of individuals who do not have extramedullary tissue involvement, lymphadenopathy/organomegaly, autoimmune disorders, or a B-cell lymphoma/leukemia. These small populations of monoclonal B cells are more common with increasing age and in males. MBL exhibits different phenotypes but is typically CD5+, resembling chronic lymphocytic leukemia (CLL), and less commonly CD5−.
Small monotypic B-cell populations (MBPs) also have been reported in bone marrow aspirates; these MBPs have been interpreted either as of unknown significance or as evidence of lymphoma even when no morphologic evidence of lymphoma was found. Therefore, we performed this retrospective study to evaluate the clinical, immunophenotypic, and histologic findings of small MBPs identified in bone marrow biopsy specimens obtained for common indications such as unexplained cytopenias, myeloid malignancies, plasma cell neoplasms, and lymphoma staging. Cases with previously diagnosed lymphoma were included in this study only when the immunophenotype of the MBPs differed from the lymphoma.