Can Monoclonal B Cell Lymphocytosis (MBCL) cause Neutropenia?

From the Guidelines

Yes, monoclonal B cell lymphocytosis (MBL) can cause neutropenia in some cases. MBL is a precursor condition to chronic lymphocytic leukemia (CLL) characterized by the presence of small clonal B cell populations in peripheral blood without other features of lymphoproliferative disorders. Neutropenia can develop in MBL through several mechanisms, including bone marrow infiltration by abnormal B cells, immune-mediated destruction of neutrophils, or as a paraneoplastic phenomenon. The risk of neutropenia increases with higher B cell counts and is more common in CLL-like MBL than other MBL subtypes.

According to the most recent guidelines, patients with MBL who develop neutropenia may require monitoring of complete blood counts, and those with severe neutropenia (absolute neutrophil count <500/μL) or recurrent infections might need intervention 1. Management options include granulocyte colony-stimulating factors for severe cases, antimicrobial prophylaxis, or in some cases, treatment directed at the underlying B cell clone if MBL is progressing toward CLL. The development of neutropenia in a patient with MBL may indicate disease progression and warrants closer clinical follow-up.

Some key points to consider in the management of neutropenia in MBL include:

• Monitoring of complete blood counts to detect neutropenia early
• Use of granulocyte colony-stimulating factors for severe neutropenia
• Antimicrobial prophylaxis to prevent infections
• Consideration of treatment directed at the underlying B cell clone if MBL is progressing toward CLL
• Close clinical follow-up to detect disease progression

It's worth noting that the evidence from older studies, such as those from 2000 1 and 2019 1, may not be directly applicable to current clinical practice, and the most recent guidelines should be followed. Additionally, the use of targeted therapies, such as venetoclax, may also impact the management of neutropenia in MBL, as outlined in recent guidelines 1.

From the Research

Monoclonal B Cell Lymphocytosis and Neutropenia

• Monoclonal B-cell lymphocytosis (MBL) is a condition characterized by the presence of a small clonal B-cell population in the peripheral blood, typically less than 5 x 10(9)/L, without lymph-node enlargement, cytopenias, or autoimmune diseases 2.
• The majority of MBL cases (75%) are classified as chronic lymphocytic leukemia (CLL)-like, and may progress into CLL at a rate of 1-2% per year 2, 3.
• MBL is not typically associated with cytopenias, including neutropenia, as it is defined by the absence of cytopenias 2, 4.
• However, patients with high-count MBL may have a higher risk of infectious complications, which could potentially lead to neutropenia 3, 5.
• There is no direct evidence to suggest that MBL causes neutropenia, but rather that it may be associated with an increased risk of infections and other complications that could lead to neutropenia 3, 5.

Key Characteristics of MBL

• MBL can be classified into low-count and high-count forms, with high-count MBL carrying a risk of progression to CLL requiring therapy of 1-2% per year 2, 3, 5.
• The immunophenotypic profile of clonal B-cells in MBL is similar to that of CLL, with the majority of cases expressing a CLL-like phenotype 2, 3.
• MBL may be diagnosed in individuals with a normal lymphocyte count via a screening assay or through the clinical evaluation of lymphocytosis 4, 6.

Clinical Management of MBL

• Patients with high-count MBL should be monitored annually for signs of progression to CLL and other complications, including infections and secondary malignancies 3, 5.
• Low-count MBL has an exceedingly small risk of progression to CLL and does not require specific follow-up 5.
• The clinical management of MBL depends on the differentiation between low-count and high-count forms, as well as the presence of other risk factors 3, 6, 5.