This important distinction between classifying a patient as having leukemia, as opposed to a pre-malignant condition should be based, at least in part, on the individual’s risk of developing clinical complications and/or dying from the disease.(20, 31) In this regard, studies have now demonstrated that the ALC threshold used in the 1988 and 1996 CLL diagnostic criteria had no relationship to either TFS or OS while the B-cell threshold proposed in the 2005 MBL diagnostic criteria strongly relates to TFS.(19, 20) As previously discussed, the risk of progression to requiring CLL specific treatment among individuals with MBL is 1–2% per year(18, 19, 25) compared to 5–7% per year for individuals with Rai stage 0 CLL.(19, 27) While this difference appears subtle it equates to a 10 year risk of requiring treatment of 7–14% for individuals with MBL compared to 50–70% for patients with Rai stage 0 CLL. Consistent with these findings, the 2008 update to the CLL diagnostic criteria incorporated a B-cell threshold of 5 x 109/L used in the 2005 MBL criteria.(26)
