The term monoclonal B-cell lymphocytosis (MBL) describes the presence of
a clonal B cell population with a count of less than 5 x 10(9)/L and no
symptoms or signs of disease. Based on the B cell count, MBL is further
classified into 2 distinct subtypes: ‘low-count’ and ‘high-count’ MBL.
High-count MBL shares a series of biological and clinical features with
chronic lymphocytic leukemia (CLL), at least of the indolent type, and
evolves to CLL requiring treatment at a rate of 1-2% per year, whereas
‘low-count’ MBL seems to be distinct, likely representing an
immunological rather than a pre-malignant condition. That
notwithstanding, both subtypes of MBL can carry ‘CLL-specific’ genomic
aberrations such as cytogenetic abnormalities and gene mutations, yet to
a much lesser extent compared to CLL. These findings suggest that such
aberrations are mostly relevant for disease progression rather than
disease onset, indirectly pointing to microenvironmental drive as a key
contributor to the emergence of MBL. Understanding microenvironmental
interactions is therefore anticipated to elucidate MBL ontogeny and,
most importantly, the relationship between MBL and CLL
