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ASH 2019: Dr. Sameer Parikh on Monoclonal B-cell Lymphocytosis, a Precursor to Chronic Lymphocytic Leukemia (CLL)

In science and medicine, information is constantly changing and may become out-of-date as new data emerge. All articles and interviews are informational only, should never be considered medical advice, and should never be acted on without review with your health care team.

One of the characteristics of chronic lymphocytic leukemia (CLL) is abnormally high levels of lymphocytes (white blood cells), particularly B cells, circulating in the blood. The medical term for this elevated number of lymphocytes is lymphocytosis. The diagnosis of CLL requires the presence of ≥5000 B-lymphocytes per microliter (5 X 109/L) circulating in the blood for at least 3 months. These must be a clonal (genetically identical) B-cell population which expresses certain specific surface markers typical for CLL that can be detected by flow cytometry.

At the annual meeting of the American Society of Hematology (ASH) 2019, Dr. John Pagel interviewed Dr. Sameer Parikh, a hematologist and oncologist at the Mayo Clinic in Rochester, MN, about monoclonal B-cell lymphocytosis and its relationship to CLL.


  • Monoclonal B-cell lymphocytosis (MBL) is a pre-malignant/pre-cancerous condition based on the number of CLL-like B cells in circulation.
  • There is an arbitrary cut-off which distinguishes CLL from MBL.
    • CLL: ≥5000 B-lymphocytes/µL blood
    • MBL: <5000 B-lymphocytes/µL blood
  • If you were to perform flow cytometry on an individual with an elevated lymphocyte count and found low numbers (<5000) of these CLL-like B cells, this would be considered MBL.
  • It is a very common condition. Approximately 5% of adults over the age of 40 would have these clonal B cells present in their body with no other apparent symptoms or abnormalities.
  • There are two types of MBL:
    • Low count MBL (<0.5 X 109/L clonal B cells)
    • High count MBL (≥5 X 109/L clonal B cells))
  • The risk of an individual with low-count MBL progressing to CLL is very low.
  • For individuals with high-count MBL, the risk of progressing to CLL, which requires therapy, is 1-2% per year. The risk of progressing is low but it increases over time.
  • Dr. Parikh is interested in studying what early changes differentiate MBL from other conditions and what causes a high-count MBL to progress to CLL.


MBL is not a disease, but it is a pre-cancerous condition which can increase the risk of developing CLL. Moving forward, what we really want to learn is what differentiates individuals who are at high risk of progression from those who are at low risk of progression. Determining this will allow doctors to provide better counseling on CLL risk and provide more intensive monitoring and counseling to those at higher risk.

Please enjoy this brief interview on a novel approach to improve the immune system with Dr. Parikh from December 2019 at ASH in Orlando, FL.

Here is a link to some of the basic science research on MBL and CLL: Tumor Mutational Load and Germline Polygenic Risk Score Predicts Time-to-First Treatment in Chronic Lymphocytic Leukemia (CLL) and High-Count Monoclonal B Cell Lymphocytosis (MBL). It is complicated article unless you have some background in the basic biology.

For those that are interested in this topic, the following articles contain more detailed information on both biology and clinical aspects of monoclonal B-cell lymphocytosis:

Monoclonal B-cell lymphocytosis and early-stage chronic lymphocytic leukemia: diagnosis, natural history, and risk stratification

Monoclonal B-Cell Lymphocytosis and Chronic Lymphocytic Leukemia

Take care of yourself first.

Ann Liu, PhD