Monoclonal B-cell lymphocytosis: definitions and natural history

Abstract

The diagnostic term monoclonal B-cell lymphocytosis (MBL) is used to characterise individuals with a circulating population of clonal B-cells, a total B-cell count of <5 x 10(9)/L, and no other features of a B-cell lymphoproliferative disorder. The clinical implications of MBL may differ depending on whether an individual with a normal lymphocyte count is identified via a screening assay (screening MBL) or identified through clinical evaluation of lymphocytosis (clinical MBL). The B-cell count used to distinguish between clinical MBL (<5 x 10(9)/L) and CLL (> or = 5 x 10(9)/L) was selected largely based on tradition and technological advances and it is unknown whether the natural history of 'clinical MBL' differs from that of patients with Rai stage 0 CLL. Since, a diagnosis of 'leukemia' may lead to profound psychologic distress for patients, we believe the diagnosis of CLL should be based on an individual's risk of developing symptoms, requiring chemotherapeutic treatment and/or dying of disease. Additional studies are needed to determine whether the clinical outcome of patients with MBL differs from that of patients with Rai stage 0 CLL and to identify what B-cell threshold optimally distinguishes between these conditions.

Long‐term follow‐up of monoclonal B‐cell lymphocytosis detected in environmental health studies

“…Each of the MBL cases reported here has unique features that provide a window into the diversity that underlies B cell biology (17) and complicates prediction of the clinical course. Our observations are consistent with previous suggestions that CLL-like MBL, in the presence of B-cell lymphocytosis, increases the risk of developing a B cell malignancy (18). These findings may well differ from those obtained in studies that were specifically designed to detect MBL using highly sensitive research methods (11,12,14,15).…”

Reassessment of small lymphocytic lymphoma in the era of monoclonal B-cell lymphocytosis

“…5,[9][10][11] Currently, a PB MBC count of 5¥10 9 /L is the WHO criterion that differentiates MBL from CLL; however, there are differences in the literature regarding the optimal B-cell thresholds that best predict the risk of progression, treatment-free survival and overall survival, with these thresholds ranging from 1.2¥10 9 /L to 11¥10 9 /L. 8,[10][11][12] Although a distinction between clinical MBL and CLL has been defined in PB, criteria for the diagnosis based on involvement of bone marrow or extramedullary tissue have not been extensively investigated. The IWCLL report states that lymphocytes typically account for more than 30% of nucleated cells in the bone marrow aspirate in patients with CLL.…”

“…[4][5][6][7][8][9] Compared to patients with CLL, patients with clinical MBL have superior treatment-free survival and longer lymphocyte doubling times. [10][11][12] While blood counts remain stable over time in the vast majority of patients with clinical MBL, progression to CLL occurs in a small proportion of patients at a rate that has been estimated to be approximately 1-2% per year. 4,5,13 The most important predictor of outcome in clinical MBL appears to be the B-cell count at diagnosis, with several studies demonstrating that the B-cell count predicts progression to CLL, treatment-free survival, and overall survival as a continuous variable.…”

Advances in the diagnosis and management of lymphoma

“…Patients with monoclonal B cells in peripheral blood at a level ,5000 cells/mm 3 and no other symptoms carry a diagnosis of monoclonal B cell lymphocytosis, and go on to develop overt CLL at a rate of 1.1% per year. 190,191 Rai stages I, II, III, and IV are characterized by lymphadenopathy, hepatosplenomegaly, anemia, and thrombocytopenia, respectively, and these stages have prognostic significance. Both cross-sectional imaging with CT and functional imaging with FDG-PET are less well established in CLL than other lymphoid malignancies, and while imaging before and after systemic treatment are recommended in guidelines, the use of routine surveillance scans has been questioned.…”