There remains great need for large, prospective MBL studies to better understand the natural history of MBL and define predictors of progression. Based on the similarities between 3(18, 19, 25) of the 4 large series(18, 19, 25, 27), our current estimate is that individuals with MBL have a 1–2% annual risk of requiring CLL-specific treatment. Future studies may identify the biologic characteristics associated with the risk of progression which in turn may allow physicians to better predict the risk of progression for a given individual. It is imperative that future prognostic studies in MBL focus not on the likelihood of the B-cell count rising above an arbitrary threshold (e.g. 5 x 109/L), but rather on the risk of developing clinically relevant outcomes such as disease related symptoms, need for treatment, or death.
