Clinical Monoclonal B Lymphocytosis (cMBL), Chronic Lymphocytic Leukemia (CLL) and Small Lymphocytic Lymphoma (SLL): Diagnostic Criteria, Features At Diagnosis and Natural History

CLL, SLL and cMBL are considered to be part of the same spectrum of clonal expansions of CD5+ B cells. Clinically, the transition from one to another of these forms over time is a well recognized event. Diagnostic criteria to separate these disorders have been proposed (IWCLL, 2008; WHO, 2008).

To compare presenting and evolving features of three groups of patients with cMBL, Rai 0 CLL or SLL and to ascertain the usefulness of current diagnostic criteria for these disorders.

Retrospective study of clinical, biologic and evolving characteristics of patients diagnosed with cMBL, Rai 0 CLL or SLL according to current criteria (CLL: ≥5x10⁹ clonal B cells/L in peripheral blood; SLL <5x10⁹/L clonal B cells with lymphadenopathy, organomegaly, cytopenia or disease-related symptoms; cMBL <5x10⁹ clonal B cells with no signs or symptoms).

Baseline characteristics of the patients are shown in the Table. Median age was 68 years (range, 24-94) and 57% of patients were males. Out of 1,093 patients, 79 had cMBL (7.2%), 522 Rai 0 CLL (48%) and 94 SLL (8.6%).

Overall, adverse biomarkers such as high LDH (p<0.001), high B2M (p<0.001), increased ZAP70 (p<0.001), high CD38 (p<0.001), unmutated IGHV status (p=0.002), +12 (p=0.02) and 11q- (p=0.01) were significantly more frequent in SLL.

In subgroup analyses, the only difference between cMBL and Rai 0 CLL was a higher proportion of cases with mutated IGHV in cMBL (p=0.008). Furthermore, when SLL was compared to Rai I to IV CLL no differences were observed (data not shown). The actuarial risk for transformation from cMBL or SLL to CLL was 4.2% and 4.4 % per year (p=0.5), respectively. Median TTFT was significantly shorter in the SLL group (12 m.) than in Rai 0 CLL (174 m.) or cMBL (244 m.) (p<0.001). Median overall survival was also significantly shorter for SLL (94 m.) compared with Rai 0 CLL and cMBL (153 and 157 m., respectively) (p=0.028). Multivariate analysis of 695 patients (cMBL/Rai 0-CLL/SLL) revealed four variables independently correlated with shorter TTFT: diagnosis of SLL vs. Rai 0 CLL vs. cMBL (HR 2.28; p=0.008), high ZAP70 (HR 4.08; p<0.001), high CD38 (HR 4.68; p=0.001) and increased serum B2M levels (HR 1.54; p = 0.031). Importantly, however, when the multivariate analysis was restricted to patients with cMBL and Rai 0 CLL, variables correlated with TTFT were the clonal B-cell count (HR 3.76; p=0.01), ZAP70 (HR 3.31; p<0.001), and CD38 (HR 4.61; p=0.02). FISH cytogenetics, IGHV mutational status,NOTCH1 or SF3B1 mutations were not included in the analysis because of missing data.

Disparities in biologic and clinical features of cMBL, CLL and SLL mainly reflect the different tumor burden in this spectrum of CD5+ monoclonal B cell disorders. In this study, the transformation rate from either cMBL or SLL to CLL was around 4% per year. As a result of differences in tumor mass, the need for therapy was shorter in SLL than in Rai 0 CLL and cMBL, and the overall survival poorer. Biologically, the only consistent difference between cMBL and Rai O CLL was a higher proportion of mutated IGHV in cMBL. Clinically, however, no differences in median survival were observed. Moreover, the clonal B cell count was the most reliable predictor of disease outcome in both cMBL and Rai 0 CLL. Therefore, the distinction between cMBL and Rai 0 CLL seems hardly justified.

No relevant conflicts of interest to declare.