Using six-color flow cytometry and IGHV gene analysis by reverse-transcriptase-polymerase-chain-reaction (RT-PCR), the authors found evidence of MBL predating the CLL diagnosis in 44 patients (98%;).(28) Notably, MBL was present up to 6.4 years prior to CLL diagnosis in these individuals. In 41 patients (91%;), the clone was confirmed by both analysis methods.(28) The IGHV gene mutation status was determined in 35 of 45 MBL clones (78%). Of these, 16 (46%) were IGHV3 subgroup genes (including 6 [17%] IGHV3-23 genes) and 9 (26%) were IGHV4 subgroup genes (including 4 [11%] IGHV4-34 genes).(28). The distribution of mutated clones as compared with unmutated clones was similar regardless of the time at which the blood samples was obtained in relationship to subsequent CLL diagnosis. Although the number of IGVH unmutated samples was small, 3 of 8 IGHV unmutated clones were present more than 3 years before the CLL diagnosis, with 2 detectable 5 years before. Thus, this study suggests that virtually all cases of CLL, including both mutated and unmutated IGHV cases, are preceded by MBL which is often present for years prior to clinical CLL diagnosis.(28)
