Clinical progression and outcome of patients with monoclonal B-cell lymphocytosis

Monoclonal B-cell lymphocytosis (MBL) is a clonal lymphoproliferation with the immunophenotype of chronic lymphocytic leukemia (CLL) but a B-lymphocyte count of less than 5 x 10(9)/l and no lymphadenopathy, organomegaly, cytopenias or symptoms. We performed a retrospective analysis of patients with MBL (n = 46), Rai stage 0 CLL (n = 112) and Rai stage > or =1 CLL (n = 54). Median follow-up and range was 30 (0.1-120) months for MBL, 60 (0.1-309) months for stage 0 CLL and 54 (0.1-309) months for stage > or =1 CLL. None of the MBL patients required treatment compared with 24 of 112 (21%) stage 0 CLL and 28 of 54 (52%) stage > or =1 CLL patients (p < 0.0003). No MBL underwent aggressive transformation compared with 1 of 112 (0.8%) stage 0 CLL and 6 of 54 (11%) stage > or =1 CLL patients (p < 0.0003). Progression-free survival (PFS) appeared improved in MBL compared to stage 0 CLL, although this did not reach statistical significant (p = 0.07) due to the relatively short follow-up in the MBL group; two year PFS was 97.2% for MBL, 93.1% for stage 0 CLL, and 68% for stage > or =1 CLL patients (p < 0.0001 for stage > or =1 CLL compared with MBL and stage 0 CLL). This is the first study of outcome in MBL which demonstrates that patients have an improved disease course compared to stage 0 CLL patients. Over a median 2.5 years of follow-up, no MBL patients required treatment or died of CLL-related causes.