From the Guidelines
Approximately 1.1% of individuals with monoclonal B cell lymphocytosis (MBL) progress to chronic lymphocytic leukemia (CLL) each year. This means that while many people may have abnormal B cell populations, only a small fraction will eventually develop CLL. The risk of progression depends on several factors, including the absolute B cell count (with higher counts conferring greater risk), genetic abnormalities such as del(13q), trisomy 12, del(11q), or del(17p), and the presence of IGHV unmutated status 1.
Key Factors Influencing Progression
- Absolute B cell count: higher counts confer greater risk
- Genetic abnormalities: del(13q), trisomy 12, del(11q), or del(17p)
- Presence of IGHV unmutated status
The progression from normal B cells to MBL and then to CLL represents a continuum, with MBL being defined as having fewer than 5,000 clonal B cells per microliter without other symptoms of lymphoproliferative disease. Most individuals with MBL remain stable without progression, which explains why CLL is relatively uncommon despite the higher prevalence of its precursor condition, particularly in older adults. According to the most recent study, the estimated rate of progression of MBL to CLL is 1.1% per year 1.
Definition and Diagnosis
- MBL: fewer than 5,000 clonal B cells per microliter without other symptoms of lymphoproliferative disease
- CLL: at least 5,000 clonal B cells/mcL (5 × 10^9/L) in the peripheral blood, established by flow cytometry quantification 1
From the Research
B Cell Progression to Chronic Lymphocytic Leukemia (CLL)
- The exact percentage of B cells that progress to CLL is not directly stated in the provided studies.
- However, a study 2 mentions that high-count Monoclonal B-cell lymphocytosis (MBL) progresses to CLL requiring therapy at a rate of 1% to 2% per year.
- It is also noted that low-count MBL rarely progresses to CLL 2.
- The studies primarily focus on the treatment and management of CLL, rather than the progression of B cells to CLL.
- A study 3 discusses the molecular pathogenesis of CLL, but does not provide information on the percentage of B cells that progress to CLL.
- Another study 4 reports on the outcomes of front-line fludarabine-cyclophosphamide-rituximab (FCR) treatment in CLL patients, but does not address the question of B cell progression to CLL.