Monoclonal B-cell lymphocytosis☆

Chronic B-cell lymphocytic leukemia (B-CLL) represents 0.9% of all new cancers. It is estimated that there will be almost 15 000 new cases and 4600 deaths due to CLL in 2015 in the USA.1 The median ages at diagnosis and death are 71 years and 80 years, respectively.1 The criteria that define the diagnosis of B-CLL include the presence of at least 5 × 106 B lymphocytes/L with the peculiar CLL phenotype, persisting in the peripheral blood for at least 3 months.2 Monoclonal B-cell lymphocytosis (MBL) is characterized by an expansion of circulating clonal B lymphocytes, totaling less than 5 × 109/L in individuals without any symptoms or signs of a lymphoproliferative disease.3,4 Three categories of MBL have been recognized: CLL-like MBL, atypical CLL-MBL, and CD5-negative MBL. Seventy-five percent of all cases are CLL-like MBL, and present the same phenotype as CLL (CD5, CD19, CD23 and CD20dim, with low surface immunoglobulin expression).3,4 Moreover, the clonal B cells in CLL-like MBL share similar chromosomal abnormalities with B-CLL. A recent systematic review reported frequencies of MBL ranging from <1% to 18.2%.5 This wide variation reflects different study populations (general population, blood donor population, outpatients from clinics and relatives of CLL patients – familial cases or sporadic cases) and the sensitivity of the multiparameter flow cytometry employed (two or three