Significant high expression of CD23 in follicular lymphoma of the inguinal region

Bridging Clinicopathologic Features and Genetics in Follicular Lymphoma: Towards Enhanced Diagnostic Accuracy and Subtype Differentiation

Follicular lymphoma (FL) is a neoplasm that originates from germinal center B cells and typically forms at least a partial follicular pattern. Approximately 85% of FL cases harbor the t(14;18)(q32;q21)/IGH::BCL2 which leads to the overexpression of BCL2. These cases are referred to as classic FL in the current World Health Organization classification [1]. These neoplasms often exhibit hallmark epigenetic deregulation due to recurrent mutations in genes such as KMT2D, CREBBP, and EZH2, with KMT2D and CREBBP considered founding events in FL lymphomagenesis. In contrast, about 15% of FL cases are negative for the t(14;18), which could present diagnostic challenges. These cases may lack the typical genetic markers and require careful pathological and molecular analysis for accurate diagnosis. This review aims to provide an up-to-date pathology resource on FL, focusing on the pathological and molecular characteristics of these neoplasms. We will detail the diagnostic criteria for FL and emphasize the importance of genetic and mutational analyses in accurately characterizing and distinguishing FL subtypes. Furthermore, we will propose methodologies and best practices for the diagnostic work-up of FL to enhance diagnostic accuracy.

The diagnostic and therapeutic challenges of Grade 3B follicular lymphoma

Grade 3B follicular lymphoma (G3B FL) is rare, accounting for only 5-10% of FLs. Not only has it been routinely excluded from clinical trials, but data published on diagnosis, outcomes, choice of therapies and role of imaging are conflicting. With the advent of increasingly diverse treatment options for low-grade (G1-3A) FL, and the molecular subcategorisation of high-grade B-cell lymphomas, characterisation and treatment of G3B FL is ever more important as extrapolation of data becomes more difficult. New data have emerged exploring unique genetic characteristics, specific features on positron emission tomography imaging, choice of therapy, and outcomes of G3B FL in the current era. The present review will summarise and appraise these new data, and offer recommendations based on current evidence.

CREBBP and STAT6 co-mutation and 16p13 and 1p36 loss define the t(14;18)-negative diffuse variant of follicular lymphoma

The diffuse variant of follicular lymphoma (dFL) is a rare variant of FL lacking t(14;18) that was first described in 2009. In this study, we use a comprehensive approach to define unifying pathologic and genetic features through gold-standard pathologic review, FISH, SNP-microarray, and next-generation sequencing of 16 cases of dFL. We found unique morphologic features, including interstitial sclerosis, microfollicle formation, and rounded nuclear cytology, confirmed absence of t(14;18) and recurrent deletion of 1p36, and showed a novel association with deletion/CN-LOH of 16p13 (inclusive of CREBBP, CIITA, and SOCS1). Mutational profiling demonstrated near-uniform mutations in CREBBP and STAT6, with clonal dominance of CREBBP, among other mutations typical of germinal-center B-cell lymphomas. Frequent CREBBP and CIITA codeletion/mutation suggested a mechanism for immune evasion, while subclonal STAT6 activating mutations with concurrent SOCS1 loss suggested a mechanism of BCL-xL/BCL2L1 upregulation in the absence of BCL2 rearrangements. A review of the literature showed significant enrichment for 16p13 and 1p36 loss/CN-LOH, STAT6 mutation, and CREBBP and STAT6 comutation in dFL, as compared with conventional FL. With this comprehensive approach, our study demonstrates confirmatory and novel genetic associations that can aid in the diagnosis and subclassification of this rare type of lymphoma.

The impact of JAK/STAT inhibitor ruxolitinib on the genesis of lymphoproliferative diseases

Background/aim

Ruxolitinib, a JAK/STAT signaling pathway inhibitor targeted drug, has been approved for the controlling of disease symptoms and splenomegaly in patients with myeloproliferative neoplastic diseases. Recently, it has been proposed that ruxolitinib-induced JAK/STAT pathway inhibition in myelofibrosis is associated with an elevated frequency of aggressive B-cell lymphomas. However, the biological basis and significance of this pharmacobiological adverse event is unknown. The aim of this bioinformatics study is to detect any possible confounding effects of ruxolitinib on the genesis of lymphoproliferative disorders.

Materials and methods

The gene expression data were retrieved from the E-MTAB-783 Cancer Genome Project database. Gene expression data for all available genes in 26 cell lines belonging to various types of lymphomas were chosen for use in this in silico analysis.

Results

We identified genes that were significant in developing resistance to ruxolitinib in lymphoma cell lines.

Conclusion

Based on the results of our present study, ruxolitinib may potentially lead to the pathological expression of the transcription factors important in lymphoma genesis, neoplastic commitment on the progenitor lymphoid cells, inhibition of repressor transcriptions protective for lymphoma development, inhibition of apoptosis, promotion of neoplastic proliferation, transcriptional activation, and proliferation of malignant neoplastic B cells.

Characterization of a variant of t(14;18) negative nodal diffuse follicular lymphoma with CD23 expression, 1p36/TNFRSF14 abnormalities, and STAT6 mutations

A predominantly diffuse growth pattern and CD23 co-expression are uncommon findings in nodal follicular lymphoma and can create diagnostic challenges. A single case series in 2009 (Katzenberger et al) proposed a unique morphologic variant of nodal follicular lymphoma, characterized by a predominantly diffuse architecture, lack of the t(14;18) IGH/BCL2 translocation, presence of 1p36 deletion, frequent inguinal lymph node involvement, CD23 co-expression, and low clinical stage. Other studies on CD23+ follicular lymphoma, while associating inguinal location, have not specifically described this architecture. In addition, no follow-up studies have correlated the histopathologic and cytogenetic/molecular features of these cases, and they remain a diagnostic problem. We identified 11 cases of diffuse, CD23+ follicular lymphoma with histopathologic features similar to those described by Katzenberger et al. Along with pertinent clinical information, we detail their histopathology, IGH/BCL2 translocation status, lymphoma-associated chromosomal gains/losses, and assessment of mutations in 220 lymphoma-associated genes by massively parallel sequencing. All cases showed a diffuse growth pattern around well- to ill-defined residual germinal centers, uniform CD23 expression, mixed centrocytic/centroblastic cytology, and expression of at least one germinal center marker. Ten of 11 involved inguinal lymph nodes, 5 solely. By fluorescence in situ hybridization analysis, the vast majority lacked IGH/BCL2 translocation (9/11). Deletion of 1p36 was observed in five cases and included TNFRSF14. Of the six cases lacking 1p36 deletion, TNFRSF14 mutations were identified in three, highlighting the strong association of 1p36/TNFRSF14 abnormalities with this follicular lymphoma variant. In addition, 9 of the 11 cases tested (82%) had STAT6 mutations and nuclear P-STAT6 expression was detectable in the mutated cases by immunohistochemistry. The proportion of STAT6 mutations is higher than recently reported in conventional follicular lymphoma (11%). These findings lend support for a clinicopathologic variant of t(14;18) negative nodal follicular lymphoma and suggests importance of the interleukin (IL)-4/JAK/STAT6 pathway in this variant.

Follicular lymphoma in young adults: a clinicopathological and molecular study of 200 patients

Follicular lymphoma is clinically heterogenous, and therefore necessitates the identification of prognostic markers to stratify risk groups and optimize clinical management. It is relatively rare in patients younger than 40 years, and the clinicopathologic characteristics and biological behavior in this age group are poorly understood. In the current study, samples from a cohort of 200 patients between 19 and 40 years were evaluated retrospectively with respect to clinical, histologic, and genetic features. These were then correlated with clinical outcome. The median age at presentation was 35 years with a slight female prepoderance (56%). Most of the cases are presented with nodal disease (90%). Concomitant follicular lymphoma and diffuse large B-cell lymphoma were observed in 7 (4%) patients. Immunohistologic studies showed the expression of CD10 (91%), BCL6 (97%), BCL2 (95%), MUM1/IRF4 (12%), MDM2 (17%), and CD23 (25%). BCL2 rearrangement was present in 74%, and BCL6 in 20%. The estimated overall survival of patients was 13 years (mean). The presence of anemia, elevated lactose dehydrogenase, bone marrow involvement, and high-risk follicular lymphoma international prognostic index correlated with adverse overall survival. Our findings revealed that follicular lymphoma in young adults demonstrate similarities with that of older adults, including the frequency of presentation at various anatomic sites, grade, and adverse prognostic factors.

The BCL2 E17 and SP66 antibodies discriminate 2 immunophenotypically and genetically distinct subgroups of conventionally BCL2-"negative" grade 1/2 follicular lymphomas

Follicular lymphoma (FL) is characterized by the translocation t(14;18)(q32;q21) resulting in constitutive overexpression of BCL2. However, in 10% to 15% of FL grade 1/2, immunohistochemical staining for BCL2 remains negative. To analyze the incidence of BCL2 negativity and the underlying molecular mechanisms in FL grade 1/2, BCL2 expression was investigated with 3 antibodies (clones 100D5, E17, SP66). The presence of a break in the BCL2 locus was determined by fluorescence in situ hybridization. The region of the BCL2 gene where the epitope of the standard BCL2 antibody resides was sequenced. Twenty-two (9.2%) of 240 identified cases of FL grade 1/2 were negative with the standard BCL2 antibody. Of these, 12 cases (55%) carried a break in the BCL2 gene locus, which, in all but one case, correlated with BCL2 expression using the alternative antibodies E17 and SP66 and with missense mutations of BCL2. Ten (45%) of the 22 cases had an intact BCL2 gene locus; 2 cases carried a BCL6/IGH translocation. All 10 cases were negative for the E17/SP66 antibodies and showed a wild-type sequence of BCL2. Six of these showed an aberrant phenotype, with CD10 negativity (30%) or CD23 expression (30%). In summary, the alternative E17/SP66 antibodies identify 2 immunohistochemically and genetically distinct subgroups of BCL2-"negative" FL grade 1/2.

CD23 expression in follicular lymphoma: clinicopathologic correlations

Follicular lymphoma (FL) is typically a CD10+/CD5-/FMC-7+ B-cell lymphoma with variable CD23 expression. The clinical significance of CD23 expression in FL is uncertain. We studied the expression of CD23 by flow cytometry in 69 lymph nodes (LNs) and correlated it with pathologic and clinical parameters. Of 69 FLs, 48 (70%) were CD23+. Grade 3 FLs were CD23- more often (12/16 [75%]) than grade 1 and 2 cases (9/53 [17%]; P < .001). CD23 expression was more common in FLs in inguinal LNs than in other sites: 20 of 23 (87%) vs 28 of 46 (61%; P = .029). Overall survival (P = .002) and event-free survival (P < .0001) were longer in the CD23+ group than in the CD23- FLs. Our study shows that grade 3 FLs are more often CD23- than lower grade FLs and that FLs in inguinal LNs are more frequently CD23+ than in LNs from other sites. Furthermore, our findings also indicate that survival is significantly better in CD23+ FLs.

A distinctive subtype of t(14;18)-negative nodal follicular non-Hodgkin lymphoma characterized by a predominantly diffuse growth pattern and deletions in the chromosomal region 1p36

Follicular lymphoma (FL) is a morphologically and genetically well-characterized B-cell non-Hodgkin lymphoma that can show predominantly follicular, combined follicular and diffuse, or predominantly diffuse growth patterns. Although approximately 85% of FLs harbor the translocation t(14;18)(q32;q21) and consistently display a follicular growth pattern, predominantly diffuse FLs are less well characterized on the phenotypical, molecular, and clinical level. We studied 35 predominantly diffuse FL by immunohistochemistry, classical chromosome banding analysis, fluorescence in situ hybridization (FISH), and gene expression profiling. A total of 28 of 29 analyzable cases lacked t(14;18), and 27 of 29 cases revealed a unifying chromosomal aberration, a deletion in 1p36. Morphologically, 12 FLs were grade 1 and 23 were grade 2, and the immunophenotype with frequent expression of CD10, BCL6, and CD23 was in line with a germinal center B-cell phenotype. The gene expression profiles of 4 predominantly diffuse FLs fell into the spectrum of typical FL, with a unique enrichment of specific gene signatures. Remarkably, patients with diffuse FL frequently presented with low clinical stage and large but localized inguinal tumors. These results suggest that predominantly diffuse FL represent a distinct subtype of t(14;18)-negative nodal FL with a unifying genetic alteration (deletion of 1p36) and characteristic clinical features.