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Transl Med UniSa. 2014 Feb 4;8:75-9. eCollection 2014 Jan.

Monoclonal B-cell lymphocytosis.

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Hematology and Stem Cell Transplantation Unit , Rionero in Vulture (Pz), Italy.
Scientific Direction, IRCCS, Centro di Riferimento Oncologico della Basilicata , Rionero in Vulture (Pz), Italy.


Monoclonal B-cell lymphocytosis (MBL) is an asymptomatic hematologic condition defined by the presence of a small (<5 x 10(9)/L) clonal B-cell population in the peripheral blood in the absence of lymph-node enlargement, cytopenias or autoimmune diseases. It is found in approximately 3-12% of normal persons depending on the accuracy of analytical techniques applied. According to the immunophenotypic profile of clonal B-cells, the majority of MBL cases (75%) are classified as chronic lymphocytic leukemia (CLL)-like. This form may progress into CLL at a rate of 1-2% per year. It is thought that CLL is always preceded by MBL. The remaining MBL cases are defined as atypical CLL-like (CD5+/CD20(bright)) and CD5(-) MBL. The MBL clone size is quite heterogenous. Accordingly, two forms of MBL are identified: i) high-count, or 'clinical' MBL, in which an evidence of lymphocytosis (<5 x 10(9)/L clonal B-cells) is seen, and ii) a low-count MBL, in which a normal leukocyte count is found and that is identified only in population-screening studies. Both forms of MBL may carry the cytogenetic abnormalities that are the hallmark of CLL, including 13q-, 17p- and trisomy 12. Consistent with the indolent phenotype of this condition, genetic lesions, such as TP53, ATM, NOTCH1 and SF3B1 mutations, usually associated with high-risk CLL, are rarely seen. Overall, no prognostic indicator of evolution of MBL to overt CLL has been found at present time. However, taking into account this possibility, a clinical and lab monitoring (at least annually), is recommended.


Monoclonal B-cell lymphocytosis; chronic lymphocytic leukemia; diagnostic criteria, management


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