Monoclonal B-cell lymphocytosis: what hematologists should know—a narrative review

Monoclonal B-cell lymphocytosis (MBL) is an asymptomatic hematologic condition characterized by the presence of clonal B-cells in the peripheral blood of otherwise healthy individuals. Initially regarded as an incidental immunophenotypic finding, MBL is now recognized as a biologically heterogeneous entity with important clinical implications, particularly as a precursor state of chronic lymphocytic leukemia (CLL). This narrative review aims to provide a comprehensive and practical overview of MBL, focusing on its epidemiology, biology, natural history, diagnostic criteria, and clinical management.