Follicular lymphoma-like B cells of uncertain significance (in situ follicular lymphoma) may infrequently progress, but precedes follicular lymphoma, is associated with other overt lymphomas and mimics follicular lymphoma in flow cytometric studies

Flow Cytometry for B-Cell Non-Hodgkin and Hodgkin Lymphomas

Multi-parametric flow cytometry is a powerful diagnostic tool that permits rapid assessment of cellular antigen expression to quickly provide immunophenotypic information suitable for disease classification. This chapter describes the classification of B-cell non-Hodgkin lymphoma (B-NHL) by flow cytometry suitable for the clinical and research environment. In addition to describing the immunophenotypic patterns of the most common B-NHL (including examples of common B-NHL), the effect of anti-CD19, -CD20, and -CD38 therapies on the evaluation of flow cytometric data is also discussed. Over the last 15 years, our laboratory has developed flow cytometry combinations that can immunophenotype classic Hodgkin lymphoma (CHL), nodular lymphocyte predominant Hodgkin lymphoma (NLPHL), and T-cell/histocyte-rich large B-cell lymphoma (THRLBCL) and the use of these assays will be presented. The CHL assay combination is also particularly well suited to immunophenotype primary mediastinal large B-cell lymphoma (PMLBCL) and our experience immunophenotyping PMLBCL by flow cytometry will be discussed. Finally, an approach to the evaluation of the reactive infiltrate of CHL, NLPHL, and THRLBCL that can provide diagnostic information will also be provided.

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.

Follicular Lymphoma in the 5th Edition of the WHO-Classification of Haematolymphoid Neoplasms-Updated Classification and New Biological Data

The conceptual description of Follicular lymphoma (FL) in the 5th edition of the World Health Organization (WHO) classification of haematolymphoid tumors (WHO-HAEM5) has undergone significant revision. The vast majority of FL (85%) with a follicular growth pattern are composed of centrocytes and centroblasts, harbor the t(14;18)(q32;q21) translocation and are now termed classic FL (cFL). They are set apart from three related subtypes, FL with predominantly follicular growth pattern, FL with unusual cytological features (uFL) and follicular large B-cell lymphoma (FLBCL). In contrast to the revised 4th edition of the WHO classification of haematolymphoid tumors (WHO-HAEM4R), grading of cFL is no longer mandatory. FL with a predominantly diffuse growth pattern had been previously recognized in WHO-HAEM4R. It frequently occurs as a large tumor in the inguinal region and is associated with CD23 expression. An absence of the IGH::BCL2 fusion and frequent STAT6 mutations along with 1p36 deletion or TNFRSF14 mutation is typical. The newly introduced subtype of uFL includes two subsets that significantly diverge from cFL: one with "blastoid" and one with "large centrocyte" variant cytological features. uFL more frequently displays variant immunophenotypic and genotypic features. FLBCL is largely identical to WHO-HAEM4R FL grade 3B and renaming was done for reasons of consistency throughout the classification. In-situ follicular B-cell neoplasm, pediatric-type FL, duodenal-type FL and primary cutaneous follicle center lymphoma are categorized as discrete entities. In addition, novel findings concerning underlying biological mechanisms in the pathogenesis of early and systemic follicular lymphoma will be presented.

Precursory or early lesions of follicular lymphoma: clinical features, pathology, and genetics

Follicular lymphoma (FL) is an indolent B-cell lymphoma with a germinal center (GC) B cell phenotype that typically harbors t(14;18)(q32;q21). t(14;18) juxtaposes IGH on 14q32 and BCL2 on 18q21, resulting in overexpression of the anti-apoptotic BCL2 protein. However, t(14;18) is also found in the peripheral blood or lymphoid nodes (LNs) of otherwise healthy individuals. Moreover, overt FL has several additional gene alterations involved in epigenetic modification, JAK/STAT signaling, immune modulation, and NF-κB signaling, indicating multi-step lymphomagenesis in FL. There are two early or precursory lesions of FL: t(14;18)-positive cells in the peripheral blood of otherwise healthy individuals and in situ follicular B-cell neoplasm (ISFN). t(14;18)-positive cells are found in 10%-50% of healthy populations, and their incidence and frequency increase with age. The detection of t(14;18) in peripheral blood is a predictive factor for an increased risk of overt FL development. In contrast, ISFN is a histopathologically recognizable precursory lesion, in which t(14;18)-positive cells are confined to the GC of otherwise reactive LNs. ISFN is usually detected incidentally, with an incidence ranging from 2.0% to 3.2%. Occasional ISFN cases have concurrent or metachronous clonally related overt FL or aggressive B-cell lymphoma of a GC phenotype. t(14;18)-positive cells in peripheral blood and isolated ISFN, by themselves, are asymptomatic with limited clinical significance; however, investigations of t(14;18)-positive precursory or early lesions offer meaningful insights into the pathogenesis of FL. This review summarizes the epidemiology, clinical features, pathology, and genetics of precursory or early lesions of FL.

B Lymphoproliferative Neoplasms of Uncertain Biological Significance: Report from the IV Workshop of the Italian Group of Hematopathology and Review of the Literature

Lymphoproliferative neoplasms of uncertain biological significance are increasingly encountered due to widespread usage of immunophenotypic and molecular techniques. Considering that clearer biological criteria and patient management have been established for B-cell lymphoproliferative diseases of undetermined significance occurring in the peripheral blood, many issues are still obscure for early lesions detected in lymphoid tissues. Regardless that some categories of lymphoproliferative neoplasms of uncertain biological significance have been recognized by the 4th edition of the WHO, other anecdotal early lymphoproliferative lesions still remain fully undefined. Some early lesions frequently originate from the germinal center, including atypical germinal centers BCL2-negative, an early pattern of large B-cell lymphoma with IRF4 rearrangement, and “in situ” high-grade B lymphomas. Moreover, other early lymphoproliferative lesions arise outside the germinal center and include those developing within the setting of monocytoid B-cell hyperplasia, but they also can be directly or indirectly associated with chronic inflammations. This review aims to summarize the concepts discussed during the IV Workshop organized by the Italian Group of Hematopathology, focus on the state-of-the-art on B-cell lymphoproliferative neoplasms of uncertain biological significance, and offer operative insights to pathologists and clinicians in routine diagnostics.

Confluent Small Bowel Lipomatosis: A Rare Cause of Recurrent Abdominal Pain

Small intestine lipomatosis is rare but may be associated with pain, intussusception, and gastrointestinal bleeding. In this report, we examine the case of a 41-year-old man who had recurrent presentations to the emergency department with non-specific abdominal pain. Preoperative imaging suggested extensive infiltration of small intestine with macroscopic fat. At surgery, extensive and confluent small bowel lipomatosis were seen. The affected ileal segment was resected, and the patient remained symptom-free after surgery. Abdominal lipomatosis is a rare condition which can be completely treated by resection of the affected gut segment but is often unsuspected and difficult to diagnose. In this report, we describe a case with the most extensive lipomatosis on record with more than 70 cm of gut with confluent lipomatosis. Magnetic resonance Enterography (MRE) is a useful non-invasive diagnostic modality, although laparoscopy/laparotomy may be necessary for assessment of the extent of disease. Symptomatic cases should be treated with segmental small bowel resection, which is curative.

Incidence, Clinicopathologic Features, and Genetics of in situ Follicular Neoplasia: A Comprehensive Screening Study in a Japanese Cohort

AIMS

In situ follicular neoplasia (ISFN) is a histologically recognisable neoplastic proliferation of follicular lymphoma (FL)-like B cells confined to the germinal centres. While some ISFNs are associated with overt FL, others are incidentally identified as isolated or pure forms in individuals without evidence of overt FL. The prevalence of incidentally found isolated ISFN is approximately 3% in Europe; however, no screening study has been conducted in Asia. To investigate the incidence and clinicopathologic characteristics of ISFNs in the Japanese population, we conducted histopathological screening of the lymph nodes (LNs) resected for solid tumours or inflammatory conditions.

METHODS AND RESULTS

We screened for ISFN in 5,700 LNs from 340 individuals using immunohistochemistry for BCL2 and identified seven ISFNs, with an incidence of 2.1%. The median age of the individuals with ISFN was 67 years, none of whom developed overt FL, with a median follow-up of 59 months. Next-generation sequencing was performed in five ISFNs, and ten variants in seven FL-associated genes were identified. The identified variants included HIST1H1E (2/5), ARID1A (2/5), KMT2D (1/5), CARD11 (1/5), BCL7A (1/5), CREBBP (1/5), and TNFRSF14 (1/5).

CONCLUSIONS

The incidence of isolated ISFN in the Japanese population is not significantly different from that in Europe, presumably reflecting the recent increase in FL in Japan. These incidentally found ISFNs have a low potential to transform into overt FL. Although mutations of FL-associated genes are already present in ISFNs, further molecular studies are needed to identify driver genes leading to the transformation of ISFN to overt FL.

Aberrant expression of CD54 detected by flow cytometry is a characteristic of B-lymphoma cells in bone marrow specimens

Background

Flow cytometry (FC) is a popular method to detect bone marrow (BM) involvement in patients with B-cell non-Hodgkin lymphoma (B-NHL). The majority of screen panels of FC still rely on finding monoclonal B-cells, e.g., B-cells with immunoglobin (Ig) light-chain restriction, which has many limitations. Therefore, exploring new markers is warranted.

Methods

A total of 52 cases of B-NHL with BM involvement were collected. The median age was 60 years. Out of these 52 cases, 34 were male, and 18 were female. A 10-color FC panel was used to detect the expression of CD54 on lymphoma cells. The expression of CD54 was calculated as the mean fluorescence index ratio (MFIR) and was described as the mean ± standard error of the mean (SEM).

Results

Up to 18/52 (34.62%) of BM specimens abnormally expressed an increased level of CD54, including 1/10 cases of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), 9/13 cases of mantle cell lymphoma (MCL), 2/14 cases of follicular lymphoma (FL), 5/9 cases of marginal zone lymphoma (MZL), and 1/3 cases of high-grade B-NHL (HG B-NHL). The expression level of CD54 was significantly increased in MCL cases (53.41 ± 11.04) compared with CLL/SLL cases (11.66 ± 2.79) and FL cases (13.49 ± 2.81). The lowest percentage of CD54-positive B-cells attained 0.13%. In 5/9 cases of MZL and 1/3 cases of HG B-NHL, increased expression of CD54 was the only abnormal immunophenotype detected besides Ig light-chain restriction. No aberrant CD54 expression was identified by FC in lymphoplasmacytic lymphoma (LPL) (0/2) and Burkitt lymphoma (BL) (0/1) cases. Aberrant expression of CD54 was not related to plasma cell differentiation.

Conclusion

Lymphoma cells, especially in MCL and MZL cases, frequently show increased expression of CD54. Such aberrant expression is not related to plasma cell differentiation. We highly recommend adding CD54 to the FC screening panel to detect BM involvement in patients with B-NHL.

Light Chain-Restricted Plasmacytoid Cells in Hyperplastic Germinal CentersA Clinicopathologic Investigation

OBJECTIVES

Follicular hyperplasias (FHs) with light chain-restricted (LCR) plasmacytoid/plasma cells (PCs) within germinal centers (GCs) based on immunohistochemistry (IHC)/in situ hybridization (ISH) can potentially lead to diagnostic error. This study aims to better characterize such cases, including their clinical implications.

METHODS

LC expression by IHC/ISH was quantitatively assessed in GCs of 17 FHs with LCRGCs. BCL2, CD10, BCL6, BCL2, immunoglobulin (Ig) heavy chains, IgG4, and Epstein-Barr encoding region stains were performed. In total, 8 cases had polymerase chain reaction (PCR)-based clonality studies.

RESULTS

All cases showed FH, including 4 with progressively transformed GCs (PTGCs); 0.8% to 52% (median, 21%) of the GCs were LCR; 13 of 17 had both κ- and λ-LCRGCs, and 4 of 17 had only κ-LCRGCs; 7 of 16 had prominent intrafollicular IgG4-positive cells. One case demonstrated BCL2-positive cells in focal LCRGCs but lacked BCL2 rearrangement. B-cell monoclonality was demonstrated in 3 of 8 cases (only after microdissection). Seven patients had autoimmune disorders, and 1 had had a transplant. Three patients had a history of lymphoma, 1 developed lymphoma, and 1 developed lymphomatoid granulomatosis subsequently.

CONCLUSIONS

FHs with LCRGC by IHC/ISH are typically not associated with the development of lymphoma, even though they can express BCL2 and show monoclonality by PCR. They may be associated with increased intrafollicular IgG4-positive cells, PTGC, and autoimmunity.

Application of CD54 in diagnosing bone marrow involvement by using flow cytometry in patients with diffuse large B-cell lymphoma

Background

Flow cytometry plays a key role in detecting bone marrow (BM) involvement in patients with diffuse large B-cell lymphoma (DLBCL). To improve its detection sensitivity, we need to explore novel markers. In this study, we detected the expression CD54 on lymphoma cells in BM specimens from DLBCL patients and clarified its diagnostic significance in BM involvement by DLBCL.

Methods

We collected BM specimens from 76 patients with DLBCL (germinal center B-cell (GCB) = 25, non-GCB = 51) and 10 control patients without lymphoma. We detected and compared the expression of CD54 on lymphoma cells and normal mature B cells by using 10-color panels.

Results

Normal plasma cells expressed a higher level of CD54 as compared with hematogones (p < 0.05) and normal mature B cells (p < 0.05). Among 76 patients, 23 of them (GCB = 12, non-GCB = 11) had BM involvement. Lymphoma B cells from 12 cases (GBC = 4, non-GCB = 8) expressed a higher level of CD54 compared to normal mature B cells (p < 0.05). Additionally, lymphoma cells of the non-GCB subtype frequently expressed a higher level of CD54 in comparison to the GCB subtype (p < 0.05). And the high expression of CD54 was not related to plasmacytoid differentiation.

Conclusion

Aberrant expression of CD54 on lymphoma cells is frequently seen in patients’ BM specimens involved by DLBCL, especially in the non-GCB subtype. CD54 could be used as a new marker to gate on lymphoma cells and improve the detection sensitivity of BM involvement in patients with DLBCL.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08753-0.

In situ follicular neoplasia: a clinicopathologic spectrum

AIMS

In situ follicular neoplasia (ISFN) occurs in ≈2-3% of reactive lymph nodes and is currently set apart from "partial involvement by follicular lymphoma" (PFL). ISFN can progress to overt lymphoma, but precise parameters to assess this risk and its association with related diseases remain incompletely understood. This study proposes to explore these parameters.

METHODS AND RESULTS

We reviewed 11 cases of ISFN and 1 of PFL between 2003 and 2018. Ten patients had ISFN in lymph nodes, one in the spleen. H&E and immunohistochemical stains were reviewed. Involvement of follicles by ISFN was scored using a 3-tier scheme. Of 5 cases with low ISFN scores, one had chronic myelomonocytic leukemia, one mycosis fungoides and three were free of hematopoietic diseases. Among them, 4 are alive and one was lost to follow-up. Of the 6 ISFN cases with high scores, 2 had concurrent marginal zone lymphomas, 1 concurrent diffuse large B-cell lymphoma (DLBCL), 1 Castleman-like disease, another progressive transformation of germinal centers with IgG4-related disease, and 1 no hematopoietic disease; all are alive except one who died of concurrent DLBCL. The patient with PFL developed DLBCL 7 years after diagnosis.

CONCLUSIONS

Based on this limited series, we conclude that only cases with high scores are associated with an overt lymphoma or an abnormal lymphoid process, and that scoring may be a useful parameter to assess risk for associated lymphoma, deserving further study. We also carried out a comprehensive review of the literature.

Lymphoma Classification

Twenty-five years after the Revised European American Classification of Lymphoid Neoplasms classification was published, its principle of an integrative approach to disease definition based on several parameters still prevails and has been adopted and expanded in the following World Health Organization classifications of tumors of the hematopoietic organs. The latest World Health Organization classification revised in 2017 comprises more than 80 entities of mature lymphoid neoplasms (B-cell, T-cell, and Hodgkin lymphomas), which are defined according to their morphology, immunophenotype, genetic lesions and molecular profiles, clinical features, and cellular derivation. The classification also recognizes both incipient and indolent lymphoid neoplasms with a low potential of progression. In this review, we highlight some of the new data and recent modifications introduced in the 2017 classification.

Scientific Advances and the Evolution of Diagnosis, Subclassification and Treatment of Lymphoma

The diagnosis of lymphoma has evolved tremendously over time. Initially, diagnosis of lymphoma was largely based on morphology alone. Over time, immunophenotyping using flow cytometry and immunohistochemistry, and then in situ hybridization, have contributed dramatically to the pathologist's ability to recognize, diagnose and subclassify lymphomas more precisely. In recent years, cytogenetic and molecular genetic techniques have developed that allow evaluation of abnormalities in lymphomas, leading to an understanding of their pathogenesis and opening the door to targeted therapies that will lead to better outcomes for lymphoma patients.

Clinicopathological features of in situ follicular neoplasm and relations with follicular lymphoma in Japan

This study aims to investigate the clinicopathological features of in situ follicular neoplasm (ISFN) in Japan. ISFN is a rare condition formerly considered as an early precursor of follicular lymphoma (FL). This is a first original report of ISFN from Asian country. We reviewed 19 biopsy samples of ISFN. ISFNs were categorized into two groups: (1) ISFN, consisting of ISFN with strong positivity for BCL-2 immunohistochemical staining (IHC), and obvious translocation of BCL-2; and (2) ISFN-like FL, featuring cases without obvious translocation but having morphological features and characteristic IHC findings of ISFN. As control, we adopted obvious FL. For some cases showing coexisting ISFN and FL lesions in the same lymph node, we could conduct further clonality analysis for each lesion. Nine of the 19 cases of ISFN coexisted with FL or had a history of overt B- or T-cell lymphoma including FL. Statistical comparison among ISFN-like FL and FL showed no significant differences in pathological features. Molecular analysis suggested that ISFN lesion and FL lesion in the same lymph node each have a different clonality. ISFN coexists or associates with other overt lymphomas frequently.

Early Events in Lymphoid Neoplasms and Indolent Follicular Lymphomas

Technical advances in diagnostic modalities have led to the characterization of indolent lymphoid disorders similar to the in situ lesions described in epithelial malignancies. These early and indolent lymphoid lesions share clinicopathologic characteristics with well-characterized lymphoid malignancies such as chronic lymphocytic leukemia and follicular lymphoma. The in situ lesions have an indolent clinical course with only a minor subset shown to progress to frank malignancies. In addition to the in situ lesions, new indolent lymphoproliferative disorders have been recently characterized. Diagnosis and characterization of these indolent lesions is necessary to prevent overtreatment with aggressive therapeutic regimens.

[Revised version of the 4th edition of the WHO classification of malignant lymphomas : What is new?]

After 8 years, the WHO has now published the updated version of the 4th edition of the classification of hematopoietic and lymphoid tumors. This update provides a conceptual rewrite of existing entities as well as some new provisional entities and categories, particularly among the aggressive B‑cell lymphomas. Important new diagnostic categories include the high-grade B‑cell lymphomas, the large B‑cell lymphoma with IRF4 rearrangement, and the Burkitt-like lymphoma with 11q aberrations. Of particular importance, new concepts concerning the taxonomy and classification of early lymphoid lesions or precursor lesions are included, such as the in situ follicular neoplasia or the in situ mantle cell neoplasia. In addition, the concept of indolent lymphoproliferations, such as breast-implant-associated anaplastic large cell lymphoma and the indolent T‑cell lymphoproliferative disorder of the gastrointestinal tract, has been strengthened. Finally, diagnostic criteria for existing lymphoma entities have been refined.

Premalignant Clonal Hematopoietic Proliferations

OBJECTIVES

The 2017 Workshop of the Society for Hematopathology/European Association for Hematopathology aimed to review premalignant clonal hematopoietic proliferations.

METHODS

The workshop panel reviewed 27 cases of clonal proliferations of indeterminate significance or potential (18 myeloid, nine lymphoid) and rendered consensus diagnoses.

RESULTS

Immunophenotyping and genetic studies on peripheral blood, bone marrow, and lymph node samples have led to the incidental detection of small clonal populations in asymptomatic individuals. These premalignant clonal myeloid and lymphoid proliferations include monoclonal gammopathy of uncertain significance, monoclonal B-cell lymphocytosis, in situ follicular neoplasia, in situ mantle cell neoplasia, clonal hematopoiesis of indeterminate potential, and clonal cytopenia of undetermined significance.

CONCLUSIONS

Current diagnostic criteria for the diagnoses of premalignant clonal hematopoietic proliferations are reviewed and discussed in the context of the cases presented at the workshop.

The current role of clinical flow cytometry in the evaluation of mature B-cell neoplasms

Flow cytometry (FC) has a well-established role in the diagnostic evaluation of mature B-cell neoplasms. Effective assessment for lineage associated antigens, aberrant antigen expression, and immunoglobulin light chain restriction requires a well-designed, optimized, and controlled FC assay. However, it is important for hematopathologists to know when flow cytometry has a more limited role, and other modalities, such as immunohistochemistry, cytogenetic and molecular testing, are more important. This review will discuss the features of an optimal FC assay for the evaluation of mature B-cell neoplasms, and the current role of FC in the diagnosis and sub-classification, prognostic assessment, identification of therapeutic targets, and assessment for disease response to therapy. © 2018 International Clinical Cytometry Society.

Diagnostically relevant updates to the 2017 WHO classification of lymphoid neoplasms

The recent 2017 WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues contains a number of updates under the category of lymphoid neoplasms. These changes include introduction of new entities, amended classification or terminology, and addition of newly discovered diagnostic and molecular features. In this review, we perform a focused, concise summary of selected lymphoid neoplasms and discuss changes in their classification. Rather than a comprehensive overview, we place specific emphasis on important and diagnostically relevant aspects of each entity that are novel or different from the previous WHO iteration and bring the practicing pathologist quickly up to speed with the updated classification.

Clinical Impact of the 2016 Update to the WHO Lymphoma Classification

OPINION STATEMENT

The 2016 revision of the WHO classification of lymphoid neoplasms includes new entities along with a clearer definition of provisional and definitive subtypes based on better understanding of the molecular drivers of lymphomas. These changes impact current treatment paradigms and provide a framework for future clinical trials. Additionally, this update recognizes several premalignant or predominantly indolent entities and underscores the importance of avoiding unnecessarily aggressive treatment in the latter subsets.

Follicular Lymphoma Diagnostic Caveats and Updates

CONTEXT.—

Follicular lymphoma is a common small B-cell lymphoma, likely to be encountered by any practicing pathologist, regardless of specialty. Although the features of typical follicular lymphoma are well known and in most instances easily identifiable, there are lesser-appreciated morphologic appearances that can raise alternative diagnostic possibilities. The limited tissue available in core needle biopsies can make it additionally challenging to thoroughly evaluate those features in the context of architecture. Furthermore, ancillary testing including immunohistochemistry and molecular/genetic analysis do not always show classic findings and may pose additional challenges to interpretation.

OBJECTIVES.—

To review the morphologic features of follicular lymphoma with a discussion of morphologic variants and mimics; to discuss pitfalls of ancillary testing and provide the practicing pathologist with an appropriate context for interpretation of immunohistochemical and molecular/genetic studies when follicular lymphoma is part of the differential diagnosis; and to propose diagnostic strategies when there is limited tissue for evaluation.

DATA SOURCES.—

We used examples of follicular lymphoma from our institution as well as a review of the literature, with a focus on the diagnostic aspects that are broadly relevant to a general pathology practice.

CONCLUSIONS.—

Follicular lymphoma can occasionally present with atypical morphologic, immunohistochemical, or molecular/genetic features. In particular, those findings can be difficult to interpret in the setting of a limited tissue sample. Awareness of those possibilities will help guide the pathologist to a more accurate and precise diagnosis.

From genetics to the clinic: a translational perspective on follicular lymphoma

Follicular lymphoma (FL) is the most frequent indolent B cell lymphoma and is still considered to be incurable. In recent years, whole-exome sequencing studies of large cohorts of patients have greatly improved our knowledge of the FL mutational landscape. Moreover, the prolonged evolution of this disease has enabled some insights regarding the early pre-lymphoma lesions as well as the clonal evolution after treatment, allowing an evolutionary perspective on lymphomagenesis. Deciphering the earliest initiating lesions and identifying the molecular alterations leading to disease progression currently represent important goals; accomplishing these could help identify the most relevant targets for precision therapy.

18F-Fluorodeoxyglucose positron emission tomography computed tomography detection threshold in follicular lymphoma: A case report

RATIONALE

Follicular Lymphoma in situ is generally identified as reactive follicular hyperplasia in which some of the hyperplastic germinal centers are colonized by few lymphoma cells. These cells can be detected through their strong 18F-Fluorodeoxyglucose avidity.

PATIENT CONCERNS

We report the case of a 70 year-old patient with arthralgia, weight loss and chronic fever over two months. A paraneoplastic polymyalgia rheumatica was initially suspected on abnormal 18F fluoro-deoxyglucose positron emission tomography (PET) pictures in two inguinal lymph nodes with a standardized uptake value at 8.6 and 5.8.

DIAGNOSES

The PET lymph nodes were removed and histological examination revealed subtle lymph nodes infiltration by follicular lymphoma in situ. The absolute number of the follicular lymphoma cells determined using virtual imaging and 3D reconstruction appeared very low with a total tumor cell volume estimated at around 0.026 mm for one lymph node and 0.041 mm for the other.

INTERVENTIONS

The patient has been treated by corticotherapy alone.

OUTCOMES

A long-time follow-up should be highly suggested for this patient to avoid any risk of clinical progression to follicular lymphoma.

LESSONS

Our findings show that low amounts of follicular lymphoma cells in reactive germinal center may reach a threshold of hypermetabolism detectable with positron emission tomography imaging, suggesting that tumor microenvironment also accounts for such as strong fluoro-deoxyglucose avidity. Thus, a systematic immunohistochemistry with anti-BCL2 antibodies should be performed on PET positive lymph node with apparent normal morphological features.

Composite Small Lymphocytic Lymphoma/Chronic Lymphocytic Leukemia and Follicular Lymphoma: A Clinicopathological Study of Six Cases

Background: Composite small lymphocytic lymphoma/chronic lymphocytic leukemia (SLL/CLL) and follicular lymphoma (FL) is extremely rare, and only 13 cases have been reported previously. Methods: We identified 6 cases of composite SLL/CLL and FL in our database and studied their clinical, histologic, immunophenotypic, and cytogenetic features. A literature review of the existing cases was also conducted. Results: The patients included 4 males and 2 females, with a median age of 72 years. Four patients presented with lymphadenopathy and 2 with extranodal diseases. Lymphocytosis was seen in 2 cases. Serum lactate dehydrogenase levels were within normal range in all but one case. There were 2 histologic patterns: SLL/CLL predominant pattern (type I) and FL predominant or mixed pattern (type II). The type I pattern was exclusively associated with in situ follicular neoplasia (ISFN). The SLL/CLL showed typical morphology and immunophenotype in all the cases. The FL component included low grade (n = 3), ISFN (n = 2), and primary cutaneous FL (n = 1). Four cases had staging bone marrow biopsies including 3 cases with involvement by SLL/CLL and 1 case with involvement by SLL/CLL and FL. Four patients received treatments, one was under clinical surveillance, and one had no available information. All patients were alive after a median follow-up of 22 months. Conclusions: This is the largest case serial of composite SLL/CLL and FL. The CL affects elderly individuals, presents with advanced clinical stage, and appears to have a relatively indolent clinical course.

A pattern-based approach to reactive lymphadenopathies

A crucial task in histopathological examination of enlarged lymph nodes is to discriminate malignant form benign processes. The central importance of this issue is reflected by the fact that benign lymphadenopathies mistaken for lymphomas belong to the most commonly misdiagnosed cancers. In addition, recognition of distinct histopathological patterns of reactive lymph node changes narrow down the potential number of causative agents, especially of those that can be specifically identified by means of often very resource-consuming ancillary techniques; thus, the more precise the differential diagnosis established upon histopathological examination is, the more targetable and efficient the application of these techniques will be. This review provides a synopsis on a histopathological pattern-based approach towards reactive lymphadenopathies.

The Pathology of Reactive Lymphadenopathies: A Discussion of Common Reactive Patterns and Their Malignant Mimics

Context.—Distinguishing between a reactive and a neoplastic lymphoid proliferation is a clinically significant task frequently performed by the surgical pathologist in routine practice.

Objectives.—To highlight common situations in lymph node pathology where reactive changes and lymphoma may be misdiagnosed.

Data Sources.—Data sources are peer-reviewed journal articles, textbooks, and clinical experience.

Conclusions.—This review aims to refresh and enhance the surgical pathologist's awareness of the shared and distinguishing features of select reactive and neoplastic lymphoproliferations, which in turn will allow the surgical pathologist to make more accurate diagnoses and avoid the pitfalls of misdiagnosis. This will be done by describing a selection of commonly encountered reactive histologic changes observed in lymph nodes, present the lymphomas with which they share overlapping features, outline the features that distinguish them, and describe an approach to making an accurate diagnosis and avoiding a misdiagnosis in each scenario.

Isolated Follicles Enriched for Centroblasts and Lacking t(14;18)/BCL2 in Lymphoid Tissue: Diagnostic and Clinical Implications

We sought to address the significance of isolated follicles that exhibit atypical morphologic features that may be mistaken for lymphoma in a background of reactive lymphoid tissue. Seven cases that demonstrated centroblast-predominant isolated follicles and absent BCL2 staining in otherwise-normal lymph nodes were studied. Four of seven cases showed clonal B-cell proliferations amid a polyclonal B cell background; all cases lacked the IGH-BCL2 translocation and BCL2 protein expression. Although three patients had invasive breast carcinoma at other sites, none were associated with systemic lymphoma up to 44 months after diagnosis. The immunoarchitectural features of these highly unusual cases raise the question of whether a predominance of centroblasts and/or absence of BCL2 expression could represent a precursor lesion or atypical reactive phenomenon. Differentiating such cases from follicular lymphoma or another mimic is critical, lest patients with indolent proliferations be exposed to unnecessarily aggressive treatment.

The 2016 revision of the World Health Organization classification of lymphoid neoplasms

A revision of the nearly 8-year-old World Health Organization classification of the lymphoid neoplasms and the accompanying monograph is being published. It reflects a consensus among hematopathologists, geneticists, and clinicians regarding both updates to current entities as well as the addition of a limited number of new provisional entities. The revision clarifies the diagnosis and management of lesions at the very early stages of lymphomagenesis, refines the diagnostic criteria for some entities, details the expanding genetic/molecular landscape of numerous lymphoid neoplasms and their clinical correlates, and refers to investigations leading to more targeted therapeutic strategies. The major changes are reviewed with an emphasis on the most important advances in our understanding that impact our diagnostic approach, clinical expectations, and therapeutic strategies for the lymphoid neoplasms.

The Expanding Spectrum of Follicular Lymphoma

Follicular lymphoma is a far more heterogeneous entity than originally appreciated. Clinical and biological variants are increasingly more granularly defined, expanding the spectrum of disease. Some variants associate with age, whereas others with anatomic site. Identification of these biologically distinct diseases has real prognostic and predictive value for patients today and likely will be more relevant in the future. Understanding of follicular lymphoma precursors has also made their identification both scientifically and clinically relevant. This review summarizes the features and understanding of follicular lymphoma, variants, and precursor lesions.

Lymphocytosis, lymphadenopathy: benign or malignant?

The increasing use of immunophenotypic and molecular analysis in the routine evaluation of patients with lymphocytosis, lymphadenopathy, or other hematologic disorders has led to the identification of unexpected small clonal lymphoid populations. These clones, sometimes with disease-specific markers, such as the t(14;18), are especially challenging for the clinician because of their unknown biologic potential and uncertain clinical behavior. Study of these early lymphoid lesions is providing important clues to the process of lymphomagenesis, and may provide the rationale for preemptive therapy in the future. More and more, the hematologist/oncologist is consulted regarding otherwise healthy individuals with lymphadenopathy and/or lymphocytosis, and pathology reports that confound the referring internist or surgeon. The report does not name a malignant lymphoproliferative disorder, but is not completely “normal”. Does the patient have a benign or malignant condition? How should they be evaluated? Is treatment indicated? These patients prove challenging for the consulting hematologist as well as the referring physician. In this review, we will focus on some of these scenarios and attempt to provide guidance for their management.

The heterogeneity of follicular lymphomas: from early development to transformation

Follicular lymphoma (FL) is a lymphoma composed of germinal center B cells, i.e., centroblasts and centrocytes, that almost always show at least a focal follicular growth pattern. Most cases have a characteristic CD5-, CD10+, BCL6+, and BCL2+ immunophenotype, and 85 % of cases exhibit the hallmark translocation t(14;18)(q32;q21) involving BCL2 and IGH. Although the typical clinicopathological findings of FL are well recognized, cases with unusual clinical, morphologic, immunophenotypic, and genetic features may pose problems in diagnosis and nomenclature. In the slide workshop organized by the European Association for Haematopathology (EAHP) and the Society for Hematopathology (SH) held in Istanbul, Turkey, unusual variants of FL were discussed based on the submitted cases, including early lesions, localized extranodal presentation, uncommon immunophenotype, rare genetic alterations, diffuse variant, and marginal zone differentiation. Interesting features such as blastoid morphology and unusual progression forms were presented, aiming to understand the genetic basis of transformation. In this report, novel findings and diagnostic challenges emerging from the submitted cases will be highlighted, and new terminologies for some of these lesions are proposed.

Early lymphoid lesions: conceptual, diagnostic and clinical challenges

There are no "benign lymphomas", a fact due to the nature of lymphoid cells to circulate and home as part of their normal function. Thus, benign clonal expansions of lymphocytes are only rarely recognized when localized. Recent studies have identified a number of lymphoid proliferations that lie at the interface between benign and malignant. Some of these are clonal proliferations that carry many of the molecular hallmarks of their malignant counterparts, such as BCL2/IGH and CCND1/IGH translocations associated with the in situ forms of follicular lymphoma and mantle cell lymphoma, respectively. There are other clonal B-cell proliferations with low risk of progression; these include the pediatric variants of follicular lymphoma and marginal zone lymphoma. Historically, early or incipient forms of T/NK-cell neoplasia also have been identified, such as lymphomatoid papulosis and refractory celiac disease. More recently an indolent form of T-cell lymphoproliferative disease affecting the gastrointestinal tract has been described. Usually, CD8(+), the clonal cells are confined to the mucosa. The clinical course is chronic, but non-progressive. NK-cell enteropathy is a clinically similar condition, composed of cytologically atypical NK-cells that may involve the stomach, small bowel or colon. Breast implant-associated anaplastic large cell lymphoma is a cytologically alarming lesion that is self-limited if confined to the seroma cavity. Atypical lymphoid proliferations that lie at the border of benign and malignant can serve as instructive models of lymphomagenesis. It is also critical that they be correctly diagnosed to avoid unnecessary and potentially harmful therapy.

CD8-positive peripheral T-cell lymphoma with aberrant expression of CD20 and concurrent in situ follicular lymphoma

A case of a 78-year-old woman with a CD8-positive peripheral T-cell lymphoma with aberrant expression of CD20 associated with follicular lymphoma in situ (FLIS) is reported. The neoplasm presented initially as cutaneous macules, papules, plaques and nodules. A skin biopsy was performed and the diagnosis of peripheral T-cell lymphoma (PTCl) with aberrant expression of CD20 was made. The staging procedures included an excisional inguinal lymph node biopsy that showed findings similar to those of the previous diagnosis. In addition, FLIS was identified. The clinicopathologic features of PTCLs with aberrant CD20 expression involving the skin as well as this uncommon association are reviewed.

Nature and importance of follicular lymphoma precursors

It is now widely recognized that cancer development is a protracted process requiring the stepwise acquisition of multiple oncogenic events. In humans, this process can take decades, if not a lifetime, blurring the notion of 'healthy' individuals. Follicular lymphoma exemplifies this multistep pathway of oncogenesis. In recent years, variants of follicular lymphoma have been recognized that appear to represent clonal B-cell expansions at an early stage of follicular lymphoma lymphomagenesis. These include follicular lymphoma in situ, duodenal follicular lymphoma, partial involvement by follicular lymphoma, and in the blood circulating follicular lymphoma-like B cells. Recent genetic studies have identified similarities and differences between the early lesions and overt follicular lymphoma, providing important information for understanding their biological evolution. The data indicate that there is already genomic instability at these early stages, even in instances with a low risk for clinical progression. The overexpression of BCL2 in t(14;18)-positive B cells puts them at risk for subsequent genetic aberrations when they re-enter the germinal center and are exposed to the influences of activation-induced cytidine deaminase and somatic hypermutations. The emerging data provide a rationale for clinical management and, in the future, may identify genetic risk factors that warrant early therapeutic intervention.

Clonal B-cell lymphocytosis exhibiting immunophenotypic features consistent with a marginal-zone origin: is this a distinct entity?

Clonal B-cell lymphocytosis of potential marginal-zone origin (CBL-MZ) rarely progresses to a well-recognized lymphoma. CBL-MZ does not require treatment in the absence of progressive disease.