New Insights into Monoclonal B-Cell Lymphocytosis

Abstract

Monoclonal B-cell lymphocytosis (MBL) is a premalignant condition characterized by the presence of less than 5000/μL circulating clonal B cells in otherwise healthy individuals. Three subcategories have been identified according to the immunophenotypic features: CLL-like, CD5(+) atypical, and CD5(−) MBL. CLL-like MBL is by far the most frequent and best studied category and further divided in low-count [LC] and high-count [HC] MBL, based on a cutoff value of 500/μL clonal B cells. LC-MBL typically remains stable and probably does not represent a truly premalignant condition, but rather an age-related immune senescence. On the other hand, HC-MBL is closely related to CLL-Rai0, bearing similar immunogenetic profile, and is associated with an annual risk of progression to CLL requiring therapy at a rate of 1.1%. Currently there are no reproducible factors for evaluating the risk of progression to CLL. CD5(−) MBL is characterized by an immunophenotype consistent with marginal zone origin and displays many similarities with marginal zone lymphomas (MZL), mainly the splenic MZL. The cutoff value of 5000/μL clonal B cells cannot probably be applied in CD5(−) MBL, requiring a new definition to describe those cases.

Detection of L265P MYD‐88 mutation in a series of clonal B‐cell lymphocytosis of marginal zone origin (CBL‐MZ)

“…Its clinical and biologic relation to CLL has been established by several studies . Moreover, on the basis of the absolute B‐cell counts, MBL is further divided into low‐count MBL and high‐count or clinical MBL . Low‐count MBL is identified in general population studies by using very sensitive flow cytometry methods and has probably no clinical relevance because, practically, it never progresses to overt disease .…”

Reply to

“…The third group of MBL is CD5(−) which has a similar immunophenotype with splenic marginal zone lymphoma. [1] As for the patient described in our case, flow cytometry (FCM) showed CD5(−), CD10(−), CD19(+), and FMC7(+), which should be assigned into the CD5(−) MBL with an origin from the marginal zone lymphoid tissue. As for the diagnosis of MBL, works should be done to exclude lymphoma because monoclonality detected by FCM can mean either MBL or any other CD5(−) lymphoma.…”

Central nervous system involvement in primary bone marrow or splenic marginal zone lymphoma: Report of two cases and review of the literature

“…MZL constitute a distinct category of mature B‐cell malignancies within the group of indolent non‐Hodgkin lymphomas, including 3 well‐defined subgroups: splenic (SMZL), extranodal MALT lymphoma, and nodal (NMZL). A clinical variant with isolated primary BM and/or blood involvement, closely related to SMZL, has been recently recognized, called primary BM MZL (PBMMZL), clonal B‐cell lymphocytosis of MZL origin, or monoclonal B‐cell lymphocytosis MZL‐like …”