Monoclonal B-cell lymphocytosis is accepted as an important risk factor for developing lymphocytosis familial chronic lymphocytic leukemia (CLL) but does not meet the criteria for B-cell lymphoproliferative disease, and patients with <5,000 (but not 0) CLL-phenotype B-cell lymphocytes per mm³. Individuals with lymphocytosis who have relatives diagnosed with CLL should undergo flow cytometry for early diagnosis. In our study, a 56-year-old patient’s brother had been early diagnosed with CLL and with lymphocytosis, and the patient was diagnosed with class 1-2 CLL after 2 years. We emphasize that individuals having a family history of CLL should be closely monitored.
Keywords: Chronic lymphocytic leukemia, familial form, monoclonal B-cell lymphocytosis