In a prospective hospital-based cohort study from the U.K., Rawston et al.(18) monitored 185 subjects with CLL-phenotype MBL and lymphocytosis for a median of 6.7 years (range 0.2 to 11.8 years) and found progressive lymphocytosis in 51 (28%). Of these, 28 (15% of the entire cohort) progressed to a diagnosis CLL. In this study, the absolute B-cell count was the only independent prognostic factor associated with progressive lymphocytosis.(18) Only 13 (7%) individuals in this cohort required chemotherapy for treatment of CLL. During the period of follow-up, 62 (34%) subjects died, however only 4 of these deaths were due to CLL. Age at enrollment greater than 68 years and hemoglobin level below 12.5 g per deciliter were the only independent prognostic factors for death(18). Thus, based on 187 cases with a median follow-up of 6.7 years, this study reported that CLL requiring treatment develops in subjects with CLL-phenotype MBL and lymphocytosis at the rate of 1.1% per year.(18)
