NODAL MARGINAL ZONE LYMPHOMA: MUTATIONAL ANALYSIS, GENE EXPRESSION PROFILE, AND DIFFERENTIAL DIAGNOSIS FROM OTHER SMALL B-CELL LYMPHOMAS

Abstract

D. Nann equally contributing author.

Objective: Nodal Marginal zone lymphoma (NMZL) represents 1.5%–1.8% of NHL. NMZL diagnosis is based on a combination of morphological and immunophenotypic features. Due to the absence of disease-defining phenotypic/genetic markers in NMZL, the differential diagnosis with other NHL, especially BCL2 rearrangement-negative follicular lymphoma (BCL2-R-neg FL) can be challenging. We performed mutational analysis to investigate whether these might help in separating NMZL from other small B-cell lymphomas. Additionally, NMZL GEP was compared to the genetic profile of BCL2-R-neg FL obtained in a previous study.

Material and Methods: 52 cases with the diagnosis of NMZL were selected. All cases were comprehensively immunophenotyped. BCL2 and BCL6 FISH analyses were performed in selected cases. Targeted NGS analysis was done on the Ion GeneStudio S5 Prime (ThermoFisher). NGS libraries were amplified using a custom Oncomine lymphoma panel (ThermoFisher) covering 82 genes frequently mutated in B-cell NHL. GEP was performed using the nCounter PanCancer Immune profiling panel from NanoString.

Results: The 52 cases included 30 women and 22 men with a mean age of 67 years (range 36–89). After morphological and mutational analyses 38 cases were confirmed as NMZL (73%) and 14 cases (27%) were reclassified as a different NHL. The most difficult differential diagnosis was with BCL2-R-neg FL (8/52; 15%), including four CD23+ cases harboring STAT6 mutations co-occurring with CREBBP and/or TNFRSF14 mutations. The other 4 cases were reclassified as BCL2-R-neg FL based on the expression of at least one GC marker and the mutational profile; 3 showed BCL6-R. Six cases (6/52; 11.5%) were reclassified as CLL based on morphology and a mutational profile compatible with CLL (ATM, BIRC3, NOTCH1, TP53). All 6 cases had an atypical phenotype, either CD5 and/or CD23 negativity. In 33/38 NMZL cases (87%), 118 pathogenic mutations were identified (3.57 mutation/per case). The most frequently mutated gene was KLF2 (13/38; 34%), followed by KMT2D (8/38; 21%), TBL1XR1, (6/38; 16%), TET2, CREBBP, HIST1H1E, BTG2, FAS (4/38; 11%), MYD88, SPEN, ARID1A, NOTCH2, TNFRSF14 (3/38; 8%), BCL10, ARID1B, ID3, HLA-B, CD70, SOCS1, (2/38; 5%), and others (see figure). Unsupervised clustering of GEP correlated with the final pathological classification and separated NMZL from the BCL2-R-neg FL STAT6 mut cases. However, some BCL2-R-neg FL STAT6 wt cases clustered with NMZL. NMZL showed upregulation of genes involved in Toll receptor cascades (TLR1, TLR7, MAP3K1), cytokine interactions (TNFSF18, CXCR3, IL6, TNFRSF15, CCR6), and innate immune system.

Conclusions: Mutational analysis is useful for the differential diagnosis of NMZL from other NHL, especially BCL2-R-neg FL and CLL with atypical phenotype. GEP demonstrated distinct signatures separating NMZL from BCL2-R-neg FL; nevertheless, some BCL2-R-neg FL STAT6 wt clustered with NMZL showing the morphological and genetic overlap of these diseases.

Research funding declaration: none

Keywords: non-Hodgkin; pathology and classification of lymphomas; indolent non-Hodgkin lymphoma

No potential sources of conflict of interest.