Differentiation on Biological Basis of Monoclonal B-Cell Lymphocytosis (MBL) From Chronic Lymphocytic Leukemia (CLL): Results of a Prospective GISL (Gruppo Italiano Studio Linfomi) Trial

Abstract 1360 The arbitrary cut-off of 5000/μL chronic lymphocytic leukemia (CLL)-phenotype cells in peripheral blood is generally used to separate monoclonal B-cell lymphocytosis (MBL) from CLL. However, a major concern is the biological differentiation, if any, between MBL and CLL. We tried to address the issue therefore analyzing 261 Rai stage 0 patients enrolled in a Gruppo Italiano Studio Linfomi (GISL) prospective multicentre trial designed to validate biological parameters in early CLL as well as to assess the impact on clinical outcome of an early versus delayed policy of treatment with subcutaneous alemtuzumab in the high biological risk. In this cohort, biological characteristics of 105 (40.2%) patients who would be reclassified as MBL using the 2008 CLL diagnostic criteria were compared with those of the remaining 156 patients who had more than 5000/μL CLL-phenotype cells in peripheral blood and fulfilled diagnostic criteria of CLL. Male to female ratio was similar for MBL and CLL (54/53 vs. 92/66, P=0.21) as was median age (58.18 vs 58.18, P=0.98). Median absolute number of cells with CLL phenotype in peripheral blood was 3120/μL (range,400-4959) in MBL and 9925/μL (range, 5020–110000) in CLL (P Disclosures: Musto: Celgene: Honoraria; Janssen Cilag: Honoraria.