Expression of germinal center cell markers by extranodal marginal zone lymphomas of MALT type within colonized follicles, a diagnostic pitfall with follicular lymphoma

The clinical significance of increased large cells in marginal zone lymphoma

Marginal zone lymphoma (MZL) is a primary, indolent small B-cell lymphoma. Subtypes include nodal, splenic, and those of extranodal mucosa-associated lymphoid tissue (MALT). These are slow growing and generally exhibit low rates of transformation to diffuse large B-cell lymphoma (DLBCL). At initial diagnosis, there can be an increase in large cells (LCs) that does not meet criteria for DLBCL. Prior studies have noted this finding, but the clinical significance of these LCs has not been well established. A total of 161 cases of MZL from 1994 to 2021 were evaluated, including all subtypes. There were 33 cases with increased LCs (>10 LCs per high-power field [hpf]), with the majority containing >15 LCs/hpf (28/33) and 128 cases without increased LCs. Cases with increased LCs were significantly more likely to have a Ki-67 proliferation index of ≥30% (P < .0001). Overall survival was not significantly different between the groups but progression-free survival was significantly worse in the LC group (P < .0001). MZL with increased LCs was also associated with a higher stage at diagnosis (P = .0035), was more likely to transform to DLBCL (P = .0016), and had a greater frequency of relapse (P < .0001). Subgroup analysis showed that both nodal and MALT LC groups had a worse progression-free survival and a higher rate of relapse than their standard nodal and MALT lymphoma counterparts, but only within the MALT subgroup did the LC cases present at a higher stage and have a higher rate of transformation to DLBCL than the standard cases. Although larger studies are needed for validation, these results suggest that the presence of LCs in MZL may serve as a useful prognostic indicator and potentially help guide clinical decision-making.

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.

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.

Histopathologic, immunophenotypic, and mutational landscape of follicular lymphomas with plasmacytic differentiation

Follicular lymphomas with plasmacytic differentiation (FL-PCD) include two major subtypes: one with predominantly interfollicular PCD that usually harbors a BCL2 rearrangement (BCL2-R), and a second that has predominantly intrafollicular PCD and the frequent absence of a BCL2-R. It is proposed that these latter cases share some features with marginal zone lymphomas (MZL). To further explore this hypothesis in an expanded cohort of FL-PCD, a clinicopathologic investigation of 25 such cases was undertaken including an analysis of their mutational landscape. The 10 interfollicular FL-PCDs exhibited typical intrafollicular centrocytes/centroblasts (90%), CD10 expression (90%), full PCD including expression of CD138 by the plasma cells (PC) (100%), and PCs with class-switched immunoglobulin heavy chains (70%). These cases were BCL2-R positive (100%), BCL6-R positive in 30%, lacked extra BCL2 copies, and only 22% had extra copies of BCL6. Similar to classic FLs, 80% of interfollicular FL-PCDs harbored mutations in epigenetic regulators KMT2D (70%), CREBBP (40%), and/or EZH2 (30%). In contrast, only 45% of 11 intrafollicular FL-PCDs demonstrated typical intrafollicular centrocytes/centroblasts, 55% were CD10(-), 80% contained IgM+ PCs, and only 27% harbored BCL2-Rs. BCL6-Rs were identified in 27% of intrafollicular FL-PCD, while 60% showed extra copies of BCL2 and 50% extra copies of BCL6, consistent with complete or partial trisomies of chromosomes 18 and 3, respectively. Only 54% of intrafollicular FL-PCDs showed mutations in epigenetic regulators. Both subtypes showed mutational differences compared to classic FL, but only the interfollicular subtype showed differences from what is reported for nodal MZL. Four additional cases showed mixed intra- and interfollicular PCD. These results suggest that FL-PCD has some distinctive features and supports the existence of two major subtypes. The interfollicular PCD subtype shares many features with classic FL. The intrafollicular FL-PCDs are more heterogeneous, have differences from classic FL, and have a greater morphologic, immunophenotypic, and genetic overlap with MZL.

Follicular lymphoma: updates for pathologists

Follicular lymphoma (FL) is the most common indolent B-cell lymphoma and originates from germinal center B-cells (centrocytes and centroblasts) of the lymphoid follicle. Tumorigenesis is believed to initiate early in precursor B-cells in the bone marrow (BM) that acquire the t(14;18)(q32;q21). These cells later migrate to lymph nodes to continue their maturation through the germinal center reaction, at which time they acquire additional genetic and epigeneticabnormalities that promote lymphomagenesis. FLs are heterogeneous in terms of their clinicopathologic features. Most FLs are indolent and clinically characterized by peripheral lymphadenopathy with involvement of the spleen, BM, and peripheral blood in a substantial subset of patients, sometimes accompanied by constitutional symptoms and laboratory abnormalities. Diagnosis is established by the histopathologic identification of a B-cell proliferation usually distributed in an at least partially follicular pattern, typically, but not always, in a lymph node biopsy. The B-cell proliferation is biologically of germinal center cell origin, thus shows an expression of germinal center-associated antigens as detected by immunophenotyping. Although many cases of FLs are typical and histopathologic features are straightforward, the biologic and histopathologic variability of FL is wide, and an accurate diagnosis of FL over this disease spectrum requires knowledge of morphologic variants that can mimic other lymphomas, and rarely non-hematologic malignancies, clinically unique variants, and pitfalls in the interpretation of ancillary studies. The overall survival for most patients is prolonged, but relapses are frequent. The treatment landscape in FL now includes the application of immunotherapy and targeted therapy in addition to chemotherapy.

Transformed diffuse large B-cell lymphoma from marginal zone lymphoma in the anterior mediastinum: A case report and review of the literature

Marginal zone lymphoma (MZL) arising from the anterior mediastinum is rare. In the majority of reported cases, the tumor was incidentally discovered, reflecting its indolent clinical features. We present a 38-year-old woman who had no medical history, and presented with a bulky anterior mediastinal tumor complicated by life-threatening compression of the vasculature and bronchi. Biopsy specimens of the neoplasm suggested transformed diffuse large B-cell lymphoma (DLBCL) from MZL. To our best knowledge, this is the first case report of anterior mediastinum MZL associated with an aggressive clinical course and life-threatening complications likely due to transformation to DLBCL.