Clonal B-Cell Lymphocytosis with Marginal Zone Features and Splenic Marginal Zone Lymphoma Share a Similar Cytogenetic and Mutational Profile

Introduction: Clonal B-cell lymphocytosis with marginal zone features (CBL-MZ) is a non-CLL type B-cell monoclonal lymphocytosis that has been recently recognized in the 2016 revision of the World Health Organization (WHO) classification of lymphoid neoplasms. Whether CBL-MZ corresponds to the early stage of splenic marginal zone lymphoma (SMZL) is not clearly defined. The aim of the study was to compare CBL-MZ and SMZL in patients diagnosed during the same period in two French university hospitals.

Methods: We performed a retrospective study including all consecutive patients with a diagnosis of CBL-MZ or SMZL between 2010 and 2014. For the purpose of the present study, all CBL-MZ and SMZL were reclassified according to the 2016 WHO classification. Patient and disease characteristics comprised clinical data, immunophenotyping of lymphocytes by flow cytometry, cytogenetic studies (G-banding and TP53 FISH) and targeted gene sequencing (TP53, NOTCH2 and MYD88). We assessed progression-free survival (PFS), lymphoma-specific survival (LSS), overall survival (OS) and cumulative incidence of histologic transformation.

Results: Forty-one patients were diagnosed with CBL-MZ (n=15) or SMZL (n=26) on consensus review. None had HCV infection. Median age was 74 years (range 43-93). At diagnosis, B symptoms (7% vs 46%, p=0.009), elevated lactate dehydrogenase (13% vs 50%, p=0.023) and elevated β2-microglobulin (50% vs 93%, p=0.039) were significantly more frequent in SMZL patients. HPLL score A was more frequent in patient with CBL-MZ (93% vs 58%, p=0.003). On lymphocyte immunophenotyping, CD23 was expressed only in SMZL (0% vs 38%, p=0.015).

Aberrant karyotype was displayed in 5/7 CBL-MZ and 15/18 of SMZL (p=0.591). Fourteen patients (56%; 2 CBL-MZ and 12 SMZL, p=0.177) had at least 3 chromosomal abnormalities and were considered to have a complex karyotype. There was no significant difference between CBL-MZ and SMZL for the frequency of detection of +3, +12, +18, del(7q) or 14q alterations. A chromosome 17p abnormality or monosomy 17 was seen in 12/25 patients (48%) without significant difference between CBL-MZ and SMZL, and was confirmed in 11/11 cases by TP53 FISH analysis (one patient had an isochromosome 17q and TP53 FISH was not done). In 11 other patients, no TP53 deletion was detected by FISH. In the 2 remaining patients (one normal karyotype and one abnormal karyotype without abnormal 17p) there was no more material for FISH analysis.

TP53 mutation was present in 1/15 (7%) CBL-MZ and 6/22 (27%) SMZL (p=0.161), NOTCH2 mutation in 1/15 (7%) CBL-MZ and 3/22 (14%) SMZL (p=0,632) and MYD88 mutation in 1/15 (7%) CBL-MZ and 3/22 (14%) SMZL (p=0.632).

After a median follow-up of 47 months (CBL-MZ, 52 months; SMZL, 46 months, p=0.771), no CBL-MZ patients had event (progression, histologic transformation or death) or started treatment, whereas 24/26 (92%) SMZL patients started a first-line treatment (chemotherapy in 62%, rituximab in 42% and/or splenectomy in 39%). Twelve SMZL patients (50% of treated patients) relapsed or progressed after the first-line treatment. Among them, 6 had histologic transformation, either in diffuse large B-cell lymphoma (DLBCL, n=5) or Hodgkin lymphoma (HL, n=1). Finally, 5 SMZL patients died (3 of DLBCL, 1 of HL, 1 of SMZL).

Overall, 4-year PFS was 100% and 31% (95% CI, 13% to 49%) for CBL-MZ and SMZL, respectively (p=0.002); 4-year LSS was 100% and 77% (95% CI, 61% to 93%) for CBL-MZ and SMZL, respectively (p=0.26); and 4-year OS was 100% and 71% (95% CI, 54% to 88%) for CBL-MZ and SMZL, respectively (p=0.25).

Clinical, laboratory, cytogenetic and molecular features were subjected to univariate analyses to evaluate their impact on PFS, LSS, OS and histologic transformation in SMZL patients. In univariate analysis for PFS, only NOTCH2 mutations and TP53 inactivation (i.e. del(17p) or TP53 mutations) predicted poorer PFS, but in multivariate analysis NOTCH2 mutations were the sole factor significantly affecting PFS rates (p=0.041). For LSS, OS and histologic transformation, no prognostic factor was identified in univariate analysis.

Conclusions: Our data suggest that CBL-MZ and SMZL share a similar cytogenetic and mutational profile. These findings suggest the possible involvement of a common oncogenic mechanism in the development of these lymphoid neoplasms.