Clonal B-Cell Lymphocytosis with Mariginal-Zone Features: Comparison with Overt Splenic Marginal-Zone Lymphomas in 77 Patients from a Monocentric Series
Authors: Merli Michele , Bianchi Benedetta , Bertù Lorenza , Ferrario Andrea , Mora Barbara , Uccella Silvia , Furlan Daniela , Tibiletti Maria Grazia , Cattaneo Simona , Sessa Fausto , Passamonti Francesco 
Published: November 2019

Diagnosis of non-CLL B Cell Chronic Lymphoproliferative Disorders (BCLPD), defined by the detection of peripheral blood (PB) B-Cell clone with flow cytometry (FC) Matutesscore≤3, is not an infrequent event in clinical daily practice. Only a portion of these cases may be actually classified according to the 2016 revision of WHO classification of lymphoid neoplasms, as in these cases a non-bone marrow (BM) tissue biopsy is rarely available due to "liquid-only disease" (BM, PB, splenomegaly) or difficult accessible sites. The two most likely diagnosis of BCLPD according to WHO 2016 are splenic marginal-zone lymphoma (SMZL) and monoclonal B Cell lymphocytosis (MBL) with non-CLL phenotype (CD19+, CD20+, SIg+, CD5-), sometimes reported as MZL-like, defined by monotypic clonal B lymphocytes (CBL) <5 x 109/l. A recent study pointed out a similar outcome regardless CBL value exceeding or not this arbitrary cut-off in strictly defined cases (absence of cytopenias, splenomegaly and adenopathy) of clonal B cell lymphocytosis with marginal-zone features (CBL-MZ) and confirmed the really indolent behaviour of this entity (Xochelli, Blood 2014).
On these bases we decided to retrospectively collect clinical, immunophenotypic, molecular features and outcome of all consecutive patients (pts) with CD5- CBL-MZ owing to the Department of Hematology of University of Insubria (Varese, Italy) from 2011 to 2019 and to compare them with overt SMZL cases. Excluding 5 SMZL pts who were splenectomized, all cases were diagnosed by means of non-BM tissue biopsy, namely BM histology and PB/BM FC, FISH and molecular studies, when appropriate, and complete laboratory and imaging staging procedures (CT scan or US).
The primary objective of the study was time to progression (TTP) for CBL-MZ group. Secondary objectives were overall survival (OS), progression-free survival (PFS) for treated pts and evaluation of early progression <24 months (Early POD) (Luminari, Blood 2019).
Overall we collected complete data of 33 pts with CD5- CBL-MZ, and 44 with SMZL (Table 1).
Focusing on CBL-MZ, FC immunophenotypic findings showed a B-Cell population with Matutes score 0 to 2 in all cases, uniform expression of B Cell antigens, namely CD19, CD20 strong, FMC7 (93%), SIg (intermediate/bright in 71%), while CD10 and CD5 were consistently negative. CD23 was expressed in 18%, CD38 in 9% and CD49b in 95%. BM sinusoidal infiltration pattern was detected in 50% of cases. TP53 mutation/deletion was detected in 4/16 pts (25%) while trisomy 12 and del13q in 1 pt each. Twenty pts presented with <5000/mmc CBL (MBL-MZ) and 13 with ≥5000/mmc CBL. With a median follow-up of 1.8 years, 6 pts (18%) progressed (4 in SMZL, 1 NMZL and 1 SLL; Fig 2) with a median TTP of 1.7 yrs (range 0.3- 12.3), while the remaining 27 remained completely stable. Among 4 pts treated, 2 received Rituximab-based regimen, both achieving CR and 2 with Chlorambucil both experiencing progression. Overall, 5 pts died (2 for progressive lymphoma), with an estimated 5-yrs of 80%.
Concerning prognostic factors, after adjusting by competing risk method, at univariate analysis age >60 yrs, CBL >5000/mmc and albumin <3.5 g/dl, were associated to shorter TTP, while age >60 yrs, Hb <11 g/dl, ECOG PS ≥2 and albumin <3.5 g/dl resulted predictive of worse OS (Table 2). By applying multivariate Cox regression model, only age >60 yrs and CBL>5000/mmc retained prognostic significance for TTP (p<0.0001), while ECOG PS ≥2 and albumin <3.5 g/dl remained independently associated with inferior OS (p<0.0001).
Considering the SMZL group, 34 pts underwent systemic treatment (rituximab-based in 32, including R-Bendamustine in 17). With a median follow-up time of 2.8 yrs, 9 pts progressed (4 of whom within 24 months from treatment initiation), with a median PFS 2.9 yrs, and 8 died (7 due to progression, including 3 DLBCL transformations) with an estimated 5-yrs OS of 79%. Notably, Early POD SMZL pts exhibited a significant increased risk of death (p<0.0001, fig.2), while in CBL-MZ did not (p=0.4).
In conclusion, CBL-MZ confirmed to be associated with indolent course and preferential evolution toward SMZL, of which it can be viewed as an initial phase or a precursor entity. In contrast with previous findings, the WHO 16 CBL cut-off defining MBL (5 x 109/l), together with advanced age, retained prognostic relevance for TTP. Finally, we confirmed for the first time in an independent series of SMZL the highly prognostic impact of Early POD24.

Disclosures
Passamonti: Roche: Consultancy; Janssen: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau.