title: [Monoclonal B-cell lymphocytosis: from literature to laboratory practice].
abstract: Monoclonal B-cell lymphocytosis (MBL) is defined as an asymptomatic condition characterized by the presence of less than 5,000 monoclonal B-cells per microliter and the absence of clinical signs or symptoms of a B-cell lymphoproliferative disorder. Most MBL cases involve B cells presenting an identical phenotype to CLL (CLL-like MBL) with a Catovsky-Matutes score of 3 to 5 and share the same chromosomal abnormalities than CLL. Depending on the absolute B cell count, one may distinguish low-count CLL-like MBL (<500 B cells/μL) which have no evidence of progression, no reduction in overall survival, no increase in infection risk and do not require any specific follow-up. Patients with clinical CLL-like MBL (>500 B cells/μL) have a 1% to 2% per year risk of progression to CLL requiring therapy, a higher risk of infectious complications and mortality implicating an annual follow-up by hematologist. MBL may also express other less common phenotypes and are named atypical MBL in case of CD5 antigen expression (Catovsky-Matutes score: 1-2) and non-CLL-like MBL for CD5 negative cases (Catovsky-Matutes score: 0-2). Their poorer prognosis implicates imaging studies, bone marrow biopsy and cytogenetic analysis in addition to physical examination in order to rule out non-hodgkinien lymphoma, and require a more frequent follow-up. This review focuses on key concepts in the classification, diagnosis, monitoring and biology of MBL in laboratory practice.
authors.affiliation: Laboratoire d'hématologie, CHU Liège, Domaine universitaire du Sart-Tilman B35, Liège, Belgique.
authors.forename: Aurore
authors.initials: A
authors.lastname: Keutgens
authors.affiliation: Laboratoire d'hématologie, CHU Liège, Domaine universitaire du Sart-Tilman B35, Liège, Belgique.
authors.forename: Jacques
authors.initials: J
authors.lastname: Foguenne
authors.affiliation: Laboratoire d'hématologie, CHU Liège, Domaine universitaire du Sart-Tilman B35, Liège, Belgique.
authors.forename: André
authors.initials: A
authors.lastname: Gothot
authors.affiliation: Laboratoire d'hématologie, CHU Liège, Domaine universitaire du Sart-Tilman B35, Liège, Belgique.
authors.forename: Françoise
authors.initials: F
authors.lastname: Tassin
mesh_terms: D001402:B-Lymphocytes / Q000473:pathology*; D019411:Clinical Laboratory Techniques / Q000379:methods; D018450:Disease Progression; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000175:diagnosis* / Q000453:epidemiology / Q000473:pathology / Q000628:therapy; D018655:Lymphocyte Count; D008218:Lymphocytosis / Q000175:diagnosis* / Q000453:epidemiology / Q000628:therapy*; D010818:Practice Patterns, Physicians'
keywords: diagnosis; evolution; monoclonal B-cell lymphocytosis