Histological criteria for selecting patients who need clonality test for non-gastric MALT lymphoma diagnosis.

The histological diagnosis of extranodal marginal zone lymphoma of the mucosa-associated lymphoid tissue (MALT lymphoma) is difficult for pathologists. Recently, digital pathology systems have been widely used to provide tools that can objectively measure lesions on slides. In this study, we measured the extent of marginal zone expansion in suspected MALT lymphoma cases and compared the results with those of a molecular clonality test. In total, 115 patients who underwent an IGH gene rearrangement test for suspected MALT lymphoma were included in this study. All cases were histologically classified into three patterns; "small lymphoid aggregates with no germinal center (Pattern 1)," "lymphoid follicles with germinal center (Pattern 2)" and " fused marginal zone or diffuse small lymphocytic proliferation (Pattern 3)." The proportions of monoclonality in Pattern 1, 2, and 3 were 25.0%, 55.0%, and 97.9%, respectively. The ratios of marginal zone thickness to germinal center diameter and entire lymphoid follicle area to germinal center area were measured in Pattern 2 cases using a digital pathology system. Combining the width cutoff of 1.5 and the areal cutoff of 3.5, the sensitivity, specificity, positive predictive value, and negative predictive value for MALT lymphoma were 96.97%, 70.37%, 80.00%, and 95.00%, respectively. In conclusion, through objective measurement of the marginal zone, suspected cases of MALT lymphoma requiring a molecular clonality test can be effectively selected.

Long-term monitoring of gastric mucosa-associated lymphoid tissue lymphoma in patients with extra copies of the MALT1 gene.

The objective of this study was to clarify the long-term prognosis of patients with gastric mucosa-associated lymphoid tissue (MALT) lymphoma with additional copies of MALT1. In this multicenter retrospective study, we enrolled 145 patients with gastric MALT lymphoma who underwent fluorescence in situ hybridization (FISH) analysis to detect t(11;18) translocation. The patient cohort was divided into three groups: Group A (n = 87), comprising individuals devoid of the t(11;18) translocation or extra MALT1 copies; Group B (n = 27), encompassing patients characterized by the presence of the t(11;18) translocation; and Group C (n = 31), including patients with extra MALT1 copies. The clinical outcomes in each cohort were collected. Over the course of a mean follow-up of 8.5 ± 4.2 years, one patient died of progressive MALT lymphoma, while 15 patients died due to etiologies unrelated to lymphoma. The progression or relapse of MALT lymphoma was observed in 11 patients: three in Group A, two in Group B, and six in Group C. In Groups A, B, and C, the 10-year overall survival rates were 82.5%, 93.8%, and 86.4%, respectively, and the 10-year event-free survival rates were 96.1%, 96.0%, and 82.9%, respectively. The event-free survival rate in Group C was significantly lower than that in Group A. However, no differences were observed in the 10-year event-free survival rates among individuals limited to stage I or II1 disease (equivalent to excluding patients with stage IV disease in this study, as there were no patients with stage II2), with rates of 98.6%, 95.8%, and 92.3% for Groups A, B, and C, respectively. In conclusion, the presence of extra copies of MALT1 was identified as an inferior prognostic determinant of event-free survival. Consequently, trisomy/tetrasomy 18 may serve as an indicator of progression and refractoriness to therapeutic intervention in patients with gastric MALT lymphoma, particularly stage IV gastric MALT lymphoma.

Splenic marginal zone lymphoma with monoclonal IgG: A case report.

RATIONALE: Splenic marginal zone lymphoma (SMZL), an indolent small B-cell lymphoma, is uncommon, and part of the patients exist plasmocytic differentiation and secrete monoclonal paraproteins including IgM predominantly. SMZL with monoclonal IgG is rarer. PATIENT CONCERNS: We report a case of SMZL (49-year-old, male) with monoclonal IgG, MYD88L265P mutation and hepatitis B virus infection. DIAGNOSES: The patient was presented to our hospital with aggravating complaints of dizziness, fatigue, postprandial abdominal distension, and night sweats. The diagnosis was confirmed by clinical manifestations, immunophenotype, bone marrow pathology. INTERVENTIONS: The patient received rituximab-based chemotherapy and sequential ibrutinib in combination with entecavir. OUTCOMES: After 1 year of follow-up, his blood routine examination had returned to normal with normal level of albumin and significantly lower globulin than before, and the spleen was of normal size. LESSONS: We conclude that rituximab-based chemotherapy is the main treatment option for the patients with SMZL, and Bruton's tyrosine kinase inhibitor has also shown beneficial efficacy.

Primary central nervous system marginal zone lymphoma.

Marginal zone lymphoma (MZL) is the most common indolent lymphoma primarily arising in the central nervous system (CNS). To date, 207 cases of primary CNS MZL (PCNSMZL) were published, mostly as single case reports or small case series. It most commonly presents as extra-axial dural-based masses, more frequently in middle-aged women, displaying an insidious onset, with a long history of symptoms preceding the diagnosis. PCNSMZL can be radiographically mistaken for meningioma. PCNSMZL consists of CD20+ , CD3- small B lymphocytes with varying degrees of plasmacytic differentiation and low proliferation index. Trisomy 3, but not MALT1 or IgH translocation, is a common genetic abnormality. Other recurrent genetic abnormalities involve TNFAIP3 and NOTCH2. Ethiopathogenesis was poorly investigated. Due to its rarity, standard of care remains to be defined; it exhibits an excellent prognosis after varied treatments, such as surgery, radiotherapy, chemotherapy or their combinations. Nevertheless, each treatment should be considered after an accurate analysis of overtreatment risk. Short follow-up is a major limitation in reported PCNSMZL cases, which restrains our knowledge on long-term results and iatrogenic sequels. This review was focussed on presentation, differential diagnoses, pathological findings, treatment options and clinical outcomes of PCNSMZL; recommendations for best clinical practice are provided.

Recognizing puzzling PD1 + infiltrates in marginal zone lymphoma by integrating clonal and mutational findings: pitfalls in both nodal and transformed splenic cases.

BACKGROUND: A marked increase in PD1-positive TFH cells in nodal MZL cases (NMZL) was reported previously and could prompt suspicion for a diagnosis of peripheral T-cell lymphoma (PTCL), especially angioimmunoblastic T-cell lymphoma (AITL). CASE PRESENTATION: To demonstrate that the pitfall might exist not only in NMZL but also in transformed splenic MZL (tSMZL), two NMZL cases (70 y/o female with enlarged left cervical lymph node and 75 y/o male with generalized lymphadenopathy) and one case of tSMZL (47 y/o male with nodal and extranodal involvement) with obvious PD1-positive T-cell hyperplasia were described here. Although all their initial diagnoses were prompted to be AITL, they were comprehensively characterized by clinical features, morphologic, immunophenotypic, clonality, and targeted exosome sequencing (TES) findings. Case 1 and Case 2 were NMZL with increased PD1 + T cells in the "peripheral pattern" or "mixed peripheral and central pattern", and Case 3 was SMZL with abundant PD1-positive T cells in the "nodular pattern" that transformed to tSMZL (DLBCL) with PD1-positive T cells distributed in the "diffuse pattern." In addition to the monoclonal IG rearrangement and polyclonal TCR rearrangement results, TES demonstrated enriched and recurrent mutations in MZLs and failed to find aberrations described in AITL- or TFH-derived lymphomas. CONCLUSIONS: It is important to realize that this pitfall can also occur in more diagnostically difficult tSMZL cases; the integration of histopathology with clonality and mutation studies is also highlighted.

The many faces of nodal and splenic marginal zone lymphomas. A report of the 2022 EA4HP/SH lymphoma workshop.

Session 3 of the lymphoma workshop of the XXI joint meeting of the European Association for Haematopathology and the Society for Hematopathology took place in Florence, Italy, on September 22, 2022. The topics of this session were splenic and nodal marginal zone lymphomas, transformation in marginal zone lymphomas, and pediatric nodal marginal zone lymphomas and their differential diagnosis as well as related entities. Forty-two cases in these categories were submitted to the workshop, including splenic lymphomas (marginal zone and diffuse red pulp lymphomas), transformed marginal zone lymphomas (splenic and nodal), nodal marginal zone lymphomas with increased TFH-cells, and pediatric nodal marginal zone lymphomas. The case review highlighted some of the principal problems in the diagnosis of marginal zone lymphomas, including the difficulties in the distinction between splenic marginal zone lymphoma, splenic diffuse red pulp lymphoma, and hairy cell leukemia variant/splenic B-cell lymphoma with prominent nucleoli which requires integration of clinical features, immunophenotype, and morphology in blood, bone marrow, and spleen; cases of marginal zone lymphoma with markedly increased TFH-cells, simulating a T-cell lymphoma, where molecular studies (clonality and mutation detection) can help to establish the final diagnosis; the criteria for transformation of marginal zone lymphomas, which are still unclear and might require the integration of morphological and molecular data; the concept of an overlapping spectrum between pediatric nodal marginal zone lymphoma and pediatric-type follicular lymphoma; and the distinction between pediatric nodal marginal zone lymphoma and "atypical" marginal zone hyperplasia, where molecular studies are mandatory to correctly classify cases.

Intracranial hematolymphoid malignancies: A case series with molecular characterization.

OBJECTIVE: Central nervous system (CNS) manifestations of hematologic malignancies are uncommon and often have a poor prognosis. As hematologic neoplasms are typically chemotherapy- and radiotherapy-sensitive, surgical resection is usually not indicated; thus, opportunities for in-depth characterization of CNS hematologic tumors are limited. Here, we report four cases of rare intracranial hematologic tumors requiring surgical intervention, allowing for histopathologic and genomic characterization. METHODS: The clinical course, genetic perturbations, and histopathological features are described for a case of 1) primary marginal zone B-cell lymphoma of the dura as well as cases of brain metastases of 2) cutaneous T-cell lymphoma, 3) acute myeloid leukemia/myeloid sarcoma, and 4) multiple myeloma. Targeted DNA sequencing, fluorescence in situ hybridization, cytogenetic analysis, flow cytometry and immunohistochemical staining were used to assess the lesions. RESULT: Molecular and histopathological characterizations of four unusual presentations of hematolymphoid diseases involving the CNS are presented. Genetic abnormalities were identified in each lesion, including chromosomal aberrations and single nucleotide variants resulting in missense or nonsense mutations in oncogenes. CONCLUSIONS: Our case series provides insight into unique pathological phenotypes of hematologic neoplasms with atypical CNS involvement. We offer targets for future studies by identifying potentially pathogenic genetic variants in these lesions, as the full implications of the novel molecular abnormalities described remain unclear.

Oncogene-induced MALT1 protease activity drives posttranscriptional gene expression in malignant lymphomas.

Constitutive mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) activity drives survival of malignant lymphomas addicted to chronic B-cell receptor signaling, oncogenic CARD11, or the API2-MALT1 (also BIRC3::MALT1) fusion oncoprotein. Although MALT1 scaffolding induces NF-κB-dependent survival signaling, MALT1 protease function is thought to augment NF-κB activation by cleaving signaling mediators and transcriptional regulators in B-cell lymphomas. However, the pathological role of MALT1 protease function in lymphomagenesis is not well understood. Here, we show that TRAF6 controls MALT1-dependent activation of NF-κB transcriptional responses but is dispensable for MALT1 protease activation driven by oncogenic CARD11. To uncouple enzymatic and nonenzymatic functions of MALT1, we analyzed TRAF6-dependent and -independent as well as MALT1 protease-dependent gene expression profiles downstream of oncogenic CARD11 and API2-MALT1. The data suggest that by cleaving and inactivating the RNA binding proteins Regnase-1 and Roquin-1/2, MALT1 protease induces posttranscriptional upregulation of many genes including NFKBIZ/IκBζ, NFKBID/IκBNS, and ZC3H12A/Regnase-1 in activated B-cell-like diffuse large B-cell lymphoma (ABC DLBCL). We demonstrate that oncogene-driven MALT1 activity in ABC DLBCL cells regulates NFKBIZ and NFKBID induction on an mRNA level via releasing a brake imposed by Regnase-1 and Roquin-1/2. Furthermore, MALT1 protease drives posttranscriptional gene induction in the context of the API2-MALT1 fusion created by the recurrent t(11;18)(q21;q21) translocation in MALT lymphoma. Thus, MALT1 paracaspase acts as a bifurcation point for enhancing transcriptional and posttranscriptional gene expression in malignant lymphomas. Moreover, the identification of MALT1 protease-selective target genes provides specific biomarkers for the clinical evaluation of MALT1 inhibitors.

Marginal zone lymphoma: 2023 update on diagnosis and management.

DISEASE OVERVIEW: Marginal zone lymphomas (MZL) are collectively the second most common type of indolent lymphoma. DIAGNOSIS: Three subtypes of MZL are recognized: splenic, extranodal, and nodal. The diagnosis is secured following biopsy of an involved nodal or extranodal site demonstrating a clonal B-cell infiltrate with CD5 and CD10 negative immunophenotype most common. Some cases will features IgM paraprotein, but MYD88 L256P mutations are less frequent than in Waldenstrom macroglobulinemia. Prognostication Several prognostic models have been developed, including the MALT-IPI and the MZL-IPI. The latter is broadly applicable across MZL subtypes and incorporates elevated serum LDH, anemia, lymphopenia, thrombocytopenia and nodal or disseminated subtypes as independent predictors of outcome. TREATMENT: We discuss suggested approach to therapy for both early and advanced-stage disease, with reference to chemo-immunotherapy, radiotherapy, and emerging treatments in relapsed/refractory disease such as BTK inhibitors.

Machine Learning Model with Texture Analysis for Automatic Classification of Histopathological Images of Ocular Adnexal Mucosa-associated Lymphoid Tissue Lymphoma of Two Different Origins.

PURPOSE: The purpose of this study was to develop artificial intelligence algorithms that can distinguish between orbital and conjunctival mucosa-associated lymphoid tissue (MALT) lymphomas in pathological images. METHODS: Tissue blocks with residual MALT lymphoma and data from histological and flow cytometric studies and molecular genetic analyses such as gene rearrangement were procured for 129 patients treated between April 2008 and April 2020. We collected pathological hematoxylin and eosin-stained (HE) images of lymphoma from these patients and cropped 10 different image patches at a resolution of 2048 × 2048 from pathological images from each patient. A total of 990 images from 99 patients were used to create and evaluate machine-learning models. Each image patch of three different magnification rates at ×4, ×20, and ×40 underwent texture analysis to extract features, and then seven different machine-learning algorithms were applied to the results to create models. Cross-validation on a patient-by-patient basis was used to create and evaluate models, and then 300 images from the remaining 30 cases were used to evaluate the average accuracy rate. RESULTS: Ten-fold cross-validation using the support vector machine with linear kernel algorithm was identified as the best algorithm for discriminating between conjunctival mucosa-associated lymphoid tissue and orbital MALT lymphomas, with an average accuracy rate under cross-validation of 85%. There were ×20 magnification HE images that were more accurate in distinguishing orbital and conjunctival MALT lymphomas among ×4, ×20, and ×40. CONCLUSION: Artificial intelligence algorithms can successfully distinguish HE images between orbital and conjunctival MALT lymphomas.

NGS-based IgH gene rearrangement monitoring predicts relapse and guides maintenance therapy in DLBCL: A case report from indolent lymphoma to aggressive lymphoma.

This report describes a case of extranodal marginal zone B-cell lymphoma (ENMZL) of the mucosa-associated lymphoid tissue (MALT) lymphoma that transformed to diffuse large B cell lymphoma (DLBCL) in a 39-year-old female patient with Hashimoto's thyroiditis (HT). The patient presented with MALT lymphoma in the thyroid tissue and DLBCL in the multiple site invasions, including the ovary, breast, and lymph nodes. We assessed the Ig gene rearrangement and mutation profile in lymphoma involved tissues and the collected stem cells. V(D)J sequence of the tumor clonotype detected in thyroid, ovary, and breast was identical, revealing a shared origin of the malignant lymphoma. Noticeably, a small percentage of tumor clonotype (the highest-ranking clonotype in tumor tissues) was detected in the stem cell sample, suggesting the malignant cells was residual in the stem cells, likely conferred disease relapse following ASCT. This patient recieved BTK inhibitor combined with radiotherapy to eradicate the residual tumor cells based on the V(D)J sequence monitoring after ASCT. Now the patient remains in complete remission following 12 months of ASCT.

Divergent evolution of metachronous follicular lymphoma and extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue from a common precursor.

The translocation t(14;18)(q32:q21)/IGH::BCL2 occurs at the pre-B stage of B-cell development in the bone marrow and is insufficient for malignant transformation, although it leads to the formation of in situ follicular B-cell neoplasia (ISFN). Despite that, the translocation is the genetic hallmark of follicular lymphoma (FL), it occurs infrequently in metachronous/synchronous lymphomas, including extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (EMZL), mantle cell lymphoma, and Hodgkin's lymphoma. In each of these scenarios, the two lymphomas often appear to be clonally related by analyses of IGH::BCL2 and/or rearranged IG genes. However, it remains largely unknown whether one lymphoma originates from the other or they develop independently. We studied five cases of metachronous EMZL and FL. In four cases, the two lymphomas were clonally related, as shown by identical IGH::BCL2 and/or rearranged IG genes or shared mutations. There were common and unique mutations between the paired EMZL and FL, indicating that they developed independently from a common premalignant cell population, harbouring IGH::BCL2 in three cases. Furthermore, case 1 presented with three metachronous FLs, and all of them originated from a common precursor cell population via divergent evolution. Our findings highlight the multi-malignant potential of IGH::BCL2-positive B-cells. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Marginal zone lymphomas.

The three main types of marginal zone lymphoma (MZL), recognized by the current lymphoma classifications are the extranodal MZL of mucosa-associated lymphoid tissue, the splenic MZL, and the nodal MZL. They share some karyotype lesions (trisomies of chromosomes 3 and 18, deletions at 6q23), and alterations of the nuclear factor kappa B (NFkB) pathway are also common in all of them. However, they differ in the presence of recurrent translocations, mutations affecting the Notch signaling pathway (NOTCH2 and less commonly NOTCH1), the transcription factors Kruppel-like factor 2 (KLF2) or the receptor-type protein tyrosine phosphatase delta (PTPRD). This review summarizes the most recent and significant advances in our understanding of the epidemiology, genetics, and biology of MZLs and outlines the current principles of the standard management of MZL at different anatomic sites.

Characterization of immune exhaustion and suppression in the tumor microenvironment of splenic marginal zone lymphoma.

The role of the tumor microenvironment (TME) and intratumoral T cells in splenic marginal zone lymphoma (sMZL) is largely unknown. In the present study, we evaluated 36 sMZL spleen specimens by single cell analysis to gain a better understanding of the TME in sMZL. Using mass cytometry (CyTOF), we observed that the TME in sMZL is distinct from that of control non-malignant reactive spleen (rSP). We found that the number of TFH cells varied greatly in sMZL, ICOS+ TFH cells were more abundant in sMZL than rSP, and TFH cells positively correlated with increased numbers of memory B cells. Treg cell analysis revealed that TIGIT+ Treg cells are enriched in sMZL and correlate with suppression of TH17 and TH22 cells. Intratumoral CD8+ T cells were comprised of subsets of short-lived, exhausted and late-stage differentiated cells, thereby functionally impaired. We observed that T-cell exhaustion was present in sMZL and TIM-3 expression on PD-1low cells identified cells with severe immune dysfunction. Gene expression profiling by CITE-seq analysis validated this finding. Taken together, our data suggest that the TME as a whole, and T-cell population specifically, are heterogenous in sMZL and immune exhaustion is one of the major factors impairing T-cell function.

Enhancing prognostication and personalizing treatment of extranodal marginal zone lymphoma.

INTRODUCTION: Extranodal marginal zone lymphoma (EMZL) of mucosa-associated lymphoid tissue is an indolent lymphoma originating from marginal zone B-cells and associated with chronic inflammation. EMZL demonstrates distinct genomic alterations according to the primary extranodal site of disease but commonly affects signaling pathways including NF-ĸB, B-cell receptor, and NOTCH. Treatment with radiation therapy is commonly implemented in localized diseases, and multiple agents are available for patients with advanced-stage diseases in need of therapy. Bendamustine with rituximab is a frontline platform associated with high efficacy. AREAS COVERED: Clinical features, diagnosis, genomics, models enabling risk stratification, treatment options, and future directions. EXPERT OPINION: The lack of consistent genotyping profile in EMZL precludes the development of tissue and circulatory biomarkers for the diagnosis, risk stratification, and monitoring of minimal residual disease. Furthermore, the biological heterogeneity observed in extranodal sites associated with overall limited genomic data prevents the testing of druggable pathways aiming for a personalized treatment approach. Future clinical trials should focus on EMZL considering the unique clinical characteristics in the eligibility criteria and response assessment to better inform efficacy of novel agents and delineate sequences of therapies.

Nodal reactive proliferation of monocytoid B-cells may represent atypical memory B-cells.

BACKGROUND: Reactive lymphadenopathies such as toxoplasmosis and cytomegalovirus lymphadenitis are associated with monocytoid cell proliferation. Monocytoid cells are B-lymphocytes with an undetermined subset. METHODS: Using digital spatial profiling whole transcriptome analyses, this study compared monocytoid and control B-cells. The B-cell subset of monocytoid cells was assigned according to gene expression profiles. RESULTS: This study identified 466 differentially expressed genes between monocytoid and control B-cells. The cellular deconvolution algorithm identified monocytoid cells as memory B-cells instead of as naïve B-cells. A comparison of the upregulated genes revealed that atypical memory B-cells had the largest number of genes overlapping with monocytoid cells compared with other memory B-cell subsets. Atypical memory B-cell markers, namely TBX21 (T-bet), FCRL4 (IRTA1), and ITGAX (CD11c), were all upregulated in monocytoid cells. Similar to atypical memory B-cells, monocytoid cells exhibited (1) upregulated transcription factors (TBX21, TOX), (2) upregulated genes associated with B-cell inhibition (FCRL5, FCRL4) and downregulated genes associated with B-cell activation (PIK3CG, NFKB1A, CD40), (3) downregulated cell cycle-related genes (CDK6, MYC), and (4) downregulated cytokine receptors (IL4R). This study also analyzed the expression of monocytoid cell signature genes in various memory B-cell subsets. Atypical memory B-cells exhibited a gene expression pattern similar to that of monocytoid cells, but other memory B-cell subsets did not. Furthermore, monocytoid cells and marginal zone lymphomas differed in gene expression profiles. CONCLUSION: Spatial transcriptomic analyses indicated that monocytoid cells may be atypical memory B-cells.

Molecular associations of response to the new-generation BTK inhibitor zanubrutinib in marginal zone lymphoma.

Using tissue whole exome sequencing (WES) and circulating tumor cell-free DNA (ctDNA), this Australasian Leukaemia & Lymphoma Group translational study sought to characterize primary and acquired molecular determinants of response and resistance of marginal zone lymphoma (MZL) to zanubrutinib for patients treated in the MAGNOLIA clinical trial. WES was performed on baseline tumor samples obtained from 18 patients. For 7 patients, ctDNA sequence was interrogated using a bespoke hybrid-capture next-generation sequencing assay for 48 targeted genes. Somatic mutations were correlated with objective response data and survival analysis using Fisher exact test and Kaplan-Meier (log-rank) method, respectively. Baseline WES identified mutations in 33 of 48 (69%) prioritized genes. NF-κB, NOTCH, or B-cell receptor (BCR) pathway genes were implicated in samples from 16 of 18 patients (89%). KMT2D mutations (n = 11) were most common, followed by FAT1 (n = 9), NOTCH1, NOTCH2, TNFAIP3 (n = 5), and MYD88 (n = 4) mutations. MYD88 or TNFAIP3 mutations correlated with improved progression-free survival (PFS). KMT2D mutations trended to worse PFS. Acquired resistance mutations PLCG2 (R665W/R742P) and BTK (C481Y/C481F) were detected in 2 patients whose disease progressed. A BTK E41K noncatalytic activating mutation was identified before treatment in 1 patient who was zanubrutinib-refractory. MYD88, TNFAIP3, and KMT2D mutations correlate with PFS in patients with relapsed/refractory MZL treated with zanubrutinib. Detection of acquired BTK and PLCG2 mutations in ctDNA while on therapy is feasible and may herald clinical disease progression. This trial was registered at https://anzctr.org.au/ as #ACTRN12619000024145.

Combined Reverse-Transcriptase Multiplex Ligation-Dependent Probe Amplification and Next-Generation Sequencing Analyses to Assign Unclassified BCL2-/BCL6- Nonrearranged Small B-Cell Lymphoid Neoplasms as Follicular or Nodal Marginal Zone Lymphoma.

Distinguishing between follicular lymphoma (FL) and nodal marginal zone lymphoma (NMZL) can be difficult when morphologic and phenotypic features are unusual and characteristic cytogenetic rearrangements are absent. We evaluated the diagnostic contribution of ancillary techniques-including fluorescence in situ hybridization (FISH)-detected 1p36 deletion; reverse-transcriptase, multiplex, ligation-dependent probe amplification (RT-MLPA); and next-generation sequencing (NGS)-for tumors that remain unclassified according to standard criteria. After review, 50 CD5-negative small B-cell lymphoid neoplasms without BCL2 and BCL6 FISH rearrangements were diagnosed as FLs (n = 27), NMZLs (n = 5), or unclassified (n = 18) based on the 2016 World Health Organization Classification of Tumours of Haematopoietic and Lymphoid Tissues. FISH helped identify the 1p36 deletion in 3 FLs and 1 unclassified tumor. Most classified FLs had an RT-MLPA germinal center B-cell (GCB) signature (93%) or were noncontributive (7%). Classified NMZLs had an RT-MLPA activated B-cell signature (20%), had an unassigned signature (40%), or were noncontributive (40%). Among unclassified tumors, the RT-MLPA GCB signature was associated with mutations most commonly found in FLs (CREBBP, EZH2, STAT6, and/or TNFRSF14) (90%). An RT-MLPA-detected GCB signature and/or NGS-detected gene mutations were considered as FL identifiers for 13 tumors. An activated B-cell signature or NOTCH2 mutation supported NMZL diagnosis in 3 tumors. Combining the RT-MLPA and NGS findings successfully discriminated 89% of unclassified tumors in favor of one or the other diagnosis. NGS-detected mutations may be of therapeutic interest. Herein, we detected 3 EZH2 and 8 CREBBP mutations that might be eligible for targeted therapies.