A retrospective analysis was conducted at Laverty Pathology; a large, non-hospital-based pathology laboratory in Sydney, Australia which provides services to both metropolitan and regional areas of New South Wales. Analysis involved studying all flow cytometry reports (27,996 patients) that were processed in the laboratory between 2015 and 2020 inclusive to identify patients with any B-cell clones. There were 3261 patients identified. Of these patients, 1977 were reported as being diagnosed with MBL and 1284 with CLL.
MBL patients were classified into two subgroups according to phenotype:
CLL-like phenotype – MBL[CLL]
Typical CLL (CD5+, CD23+, CD200+, CD43+, weak CD20 and CD22, weak SIg)
Atypical CLL (CD5+, strong CD20, CD22 or SIg, CD23- or CD200-)
Other clonal B-cell (non-CLL) phenotypes (CD5-) – MBL[non-CLL]
MBL (60.6%) is more common than CLL (39.4%). The majority of MBL have a typical CLL-like phenotype (63.7%) (Table 2). The age distribution is very similar between MBL and CLL, with a very low incidence <40 years (~1%) and the highest incidence 60-79 years (~57-63%). The male (M) to female (F) ratio is higher in CLL (M:F 1.6:1) than MBL (M:F 1.2:1).
Most MBL cases are HC-MBL (~67%) and ~5.5% progressed to CLL (~0.9% per year). LC-MBL were 28% of MBL cases detected with a ‘CLL-like’ B-cell count below 0.5x109/L, with 10.6% having fewer than 0.05x109 clonal B-cells/L. Most LC-MBL persisted over long periods without progression; of 654 patients with LC-MBL analysed, 3 progressed to CLL and 1 to MCL (~0.10% per year). More frequent progression to CLL occurs in atypical CLL-like MBL phenotype (3.5%) compared to typical CLL-like MBL phenotype (1.1%).