Immunoarchitectural patterns of progressive transformation of germinal centers with and without nodular lymphocyte-predominant Hodgkin lymphoma

Pitfalls in Lymph Node Fine Needle Aspiration Cytology

BACKGROUND

Fine needle aspiration cytology (FNAC) is an accurate, minimally invasive, and cost-effective biopsy method for enlarged lymph nodes. While the role of lymph node FNAC in the diagnosis of infectious or reactive conditions and metastatic malignancy is unquestioned, differing views still exist on its role in the diagnosis of lymphoma. Nevertheless, regardless of the practice setting, pitfalls and potential for error exist, and it is incumbent upon the pathologist to be aware of these pitfalls, as this is the first line of defence against errors.

SUMMARY

This discussion will focus on potential interpretational errors, specifically highlighting scenarios leading to false-negative and false-positive diagnosis and errors in tumour classification, with an emphasis on cytomorphology. Potential entities that may fly below the radar of the pathologist - so-called off-radar entities - are also discussed, as a reminder to consider broad differentials in cases with unusual morphologic features. Some reasons for false-negative diagnoses include low-grade lymphomas that mimic a mixed, polymorphous reactive lymphoid population or aspirates with a paucity of lesional cells, through either sampling error or the intrinsic nature of the entity, e.g., nodular lymphocyte predominant Hodgkin lymphoma. Some of the potential causes of false-positive diagnoses that are discussed include viral-associated lymphadenopathy, Kikuchi-Fujimoto lymphadenitis, or benign adnexal lesions mimicking metastatic malignancy. Errors in tumour classification covered include metastatic carcinoma, sarcoma, melanoma, and lymphoma mimicking each other, and Hodgkin lymphoma and its mimics. Finally, less common entities such as follicular dendritic cell sarcoma and others are briefly mentioned, to remind us of conditions that may slip under our diagnostic radar.

KEY MESSAGES

A systematic review of diagnostic pitfalls and traps is elucidated here, with some tips to avoid these traps. The triple approach to the diagnostic workup is emphasised, which includes rigorous clinicopathologic correlation, attention to cytomorphology, and judicious application of ancillary tests.

Reactive Lymphadenopathy in the Pediatric Population with a Focus on Potential Mimics of Lymphoma

Benign lymphadenopathy is common in the pediatric population and may be clinically striking. As in adults, lymph node evaluation in pediatric patients requires careful morphologic and immunohistochemical assessment and clinical contextualization of the findings. It is important for the pathologist to be familiar with benign and reactive conditions that may mimic malignancy. This review presents non-neoplastic or indolent processes or patterns of lymphoid hyperplasia that may be confused with or raise the differential of lymphoma, with a focus on those more commonly encountered in the pediatric/adolescent population.

How I approach: The workup and management of patients with progressive transformation of the germinal center

Progressive transformation of the germinal center (PTGC) is a common and underrecognized cause of pediatric lymphadenopathy. PTGC may be associated with numerous systemic medical conditions that require further workup and management, including malignancy, autoimmune conditions, lymphoproliferative conditions, immunodeficiency, and infection. Given the breadth and rarity of the associated conditions, workup should be tailored to the individual patient and occur in a tiered approach. Patients with PTGC require ongoing follow-up, given their long-term risk of malignancy and recurrent PTGC.

[Reactive lymphadenopathies]

The human body comprises around 600 lymph nodes as constituents of a decentralized and dispersed immune system. The main task of lymph nodes is cleaning the lymph fluid and defending the organism against outer and inner threats by bacteria, viruses and tumour cells. The histologic picture of lymph nodes reflects the different strategies of the innate and adaptive immune system, which allocates antigen presenting cells, macrophages, B‑ and T‑cell systems and reticulum cells. However, the histological picture, without any additional investigations, usually only allows speculation about the causative agent like toxoplasmosis, other bacteria or viruses. This chapter describes different lymph node reactions in detail in order to obtain a better understanding of specific immune reactions allowing a precise diagnosis and a reliable distinction from malignant processes. The last issue in particular is one of the main tasks of haematopathology. In addition to these known principles, we try to integrate results obtained with the new method of three-dimensional (3D) microscopy of fixed lymphoid tissue. At first glance, this seems to be unusual. Nevertheless, we try to apply this approach, since 3D visualization of morphological details provides distinct cellular details as well as new interpretations of cell-cell interactions and the functions of lymphoid compartments, like germinal centres and T‑zones.

Chronic Generalized Lymphadenopathy in a Child—Progressive Transformation of Germinal Centers (PTGC)

Background: Enlarged lymph nodes are a common complaint in a Pediatrician’s office. Diagnosis of reactive lymphadenopathy secondary to infectious, inflammatory, immune dysregulation calls for clinical investigation, including a thorough history, physical exam, imaging, and less often, a biopsy of the lymph node. Here we discuss a rare presentation of extensive generalized, chronic, waxing, and waning lymphadenopathy diagnosed as Progressive Transformation of Germinal Centers (PTGC) and the course of illness over eight years follow up period. Discussion: Progressive Transformation of Germinal Centers (PTGC) is considered a benign condition, but extensive recurrent generalized lymphadenopathy in a very young child has not been reported before. This case demonstrates the importance of long-term follow-up and tailoring the diagnostic work-up and management based on new signs and symptoms. Here we focus on the clinical considerations and management of complex presentation of a common clinical finding.

Fine-Needle Aspiration Diagnosis of Lymphoma Based on Cytomorphology Alone: How Accurate is it? - A Cyto-Histopathology Correlative Study

Context:

Fine-needle aspiration cytology (FNAC) is a rapid and accurate first-line diagnostic modality in lymphadenopathy.

Aims:

To determine the utility of FNAC for the diagnosis of lymphoma and highlight the various pitfalls in morphological interpretation.

Settings and Design:

This was a retrospective study of 3 years duration in which cytology diagnosis was compared with the follow-up histopathology diagnosis wherever available.

Results:

A cytodiagnosis of lymphoma was made in a total of 868 cases (2.8%) out of nearly 33,000 FNAC performed during the study period; 556 (64.1%) cases were diagnosed as non-Hodgkin lymphoma (NHL), 198 (22.8%) as Hodgkin lymphoma (HL), and in 114 (13.1%) cases, a cytological diagnosis of lymphoma without further categorization was given. Histopathological reports were available in 348 cases, with an overall concordance rate of 93.1% (324), which was slightly higher in the HL cases (95.8%) as compared to NHL (91.7%). Twenty-four cases (6.9%) showed discordant cytological diagnosis with subsequent histopathology. The main reasons for the erroneous diagnosis were the over-interpretation of the germinal center cells as atypical lymphoid cells, over-interpretation of immunoblasts with prominent nucleoli as Hodgkin cells, and sheets of monomorphic lymphoid cells interpreted as low-grade lymphoma.

Conclusion:

Cytomorphology alone can make a correct basic diagnosis of lymphoma with a high degree of accuracy. The errors in interpretation can be further reduced by careful attention to the diagnostic pitfalls and common differential diagnoses.

Flow Cytometric Detection of the Double-Positive (CD4+CD8+)/PD-1bright T-Cell Subset Is Useful in Diagnosing Nodular Lymphocyte-Predominant Hodgkin Lymphoma

CONTEXT.—

Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) is characterized by neoplastic lymphocyte-predominant cells frequently rimmed by CD3+/CD57+/programmed death receptor-1 (PD-1)+ T cells. Because of the rarity of lymphocyte-predominant cells in most cases, flow cytometric studies on NLPHL often fail to show evidence of malignancy.

OBJECTIVE.—

To evaluate the diagnostic utility of PD-1 in detecting NLPHL by flow cytometry, in conjunction with the CD4:CD8 ratio and the percentage of T cells doubly positive for CD4 and CD8.

DESIGN.—

Flow cytometric data obtained from cases of NLPHL (n = 10), classical Hodgkin lymphoma (n = 20), B-cell non-Hodgkin lymphoma (n = 22), T-cell non-Hodgkin lymphoma (n = 5), benign lymphoid lesions (n = 20), angioimmunoblastic T-cell lymphomas (n = 6) and T-cell/histiocyte-rich large B-cell lymphomas (n = 2) were analyzed and compared.

RESULTS.—

Compared with the other groups, NLPHL showed significantly higher values in the following parameters: CD4:CD8 ratio, percentage of T cells doubly positive for CD4 and CD8, percentage of PD-1-positive T cells, and median fluorescence intensity of PD-1 expression in the doubly positive for CD4 and CD8 subset. Using a scoring system (0-4) based on arbitrary cutoffs for these 4 parameters, all 10 NLPHL cases scored 3 or higher, as compared with only 3 cases from the other groups, producing an overall sensitivity of 100% and a specificity of 96% (72 of 75). Two of the 3 outliers were non-Hodgkin lymphoma, and both showed definitive immunophenotypic abnormalities leading to the correct diagnosis. The remaining outlier was a case of T-cell/histiocyte-rich large B-cell lymphoma.

CONCLUSIONS.—

The inclusion of anti-PD-1 in flow cytometry is useful for detecting NLPHL in fresh tissue samples, most of which would have otherwise been labeled as nondiagnostic or reactive lymphoid processes.

Pitfalls in the Diagnosis of Nodular Lymphocyte Predominant Hodgkin Lymphoma: Variant Patterns, Borderlines and Mimics

Simple Summary

Nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) is a rare lymphoma containing infrequent tumor cells (LP cells) in a background of non-neoplastic cells. Some cases of NLPHL can recur or progress to a more aggressive lymphoma, such as diffuse large B-cell lymphoma. Awareness of the different appearances of NLPHL and its overlap with other lymphomas are important for the appropriate diagnosis, classification and research. This article discusses the conceptual framework and guidelines for the diagnosis of NLPHL, and how NLPHL can be best separated from its mimics. Emerging data in the field point to genetic changes in LP cells that are shaped by immune mechanisms. In addition, non-neoplastic cells in the background of LP cells also appear to play an important role. Further investigation is necessary to fully understand the biology of NLPHL and personalize cancer care for patients affected by this lymphoma.

Abstract

Nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) represents approximately 5% of Hodgkin lymphoma and typically affects children and young adults. Although the overall prognosis is favorable, variant growth patterns in NLPHL correlate with disease recurrence and progression to T-cell/histiocyte-rich large B-cell lymphoma or frank diffuse large B-cell lymphoma (DLBCL). The diagnostic boundary between NLPHL and DLBCL can be difficult to discern, especially in the presence of variant histologies. Both diagnoses are established using morphology and immunophenotype and share similarities, including the infrequent large tumor B-cells and the lymphocyte and histiocyte-rich microenvironment. NLPHL also shows overlap with other lymphomas, particularly, classic Hodgkin lymphoma and T-cell lymphomas. Similarly, there is overlap with non-neoplastic conditions, such as the progressive transformation of germinal centers. Given the significant clinical differences among these entities, it is imperative that NLPHL and its variants are carefully separated from other lymphomas and their mimics. In this article, the characteristic features of NLPHL and its diagnostic boundaries and pitfalls are discussed. The current understanding of genetic features and immune microenvironment will be addressed, such that a framework to better understand biological behavior and customize patient care is provided.

Evolutionary clonal trajectories in nodular lymphocyte predominant Hodgkin lymphoma with high transformation risk

The B cell architecture of nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) is complex since it is composed of malignant lymphocyte-predominant (LP) cells along with a B cell rich bystander environment. To gain insight into molecular determinants of transformation, we studied B cell evolutionary trajectories in lymphoma tissue from diagnosis to relapse or transformation to non-Hodgkin lymphoma by immunoglobulin heavy chain next-generation sequencing. NLPHL cases that later transformed showed higher age, IgD negativity, absence of the characteristic IGHV3/IGHD3/IGHJ6 LP rearrangement and high repertoire clonality. We constructed phylogenetic trees within the compartment of the malignant clone to investigate clonal evolution. In all relapsing cases, the LP rearrangement was identical at diagnosis and relapse. NLPHL cases with transformation showed more complex trajectories with strong intraclonal diversification. The dominant founder clone in transformations showed clonal evolution, if derived from the same cell of origin, or originated from a different cell of origin. Together, our data point to a significant role of antigenic drive in NLHPL transformations and identify high B cell repertoire clonality with dominant intraclonal LP cell diversification as a hallmark of transformation. Sequencing of the initial paraffin-embedded tissue may therefore be diagnostically applied to identify NLPHL cases with high transformation risk.

Role of FNA with core biopsy or cell block in patients with nodular lymphocyte-predominant Hodgkin lymphoma

BACKGROUND

Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) represents a diagnostic challenge on surgical excisional or incisional biopsy. Classification is further challenging on fine needle aspiration (FNA) material accompanied by needle core and/or cell block biopsy (FNA+core/CB).

METHODS

The authors studied all FNA+core/CB and surgical excisional or incisional biopsies to evaluate for lymphoma in patients who had a prior history of NLPHL or subsequent diagnosis of NLPHL over a 5-year period from 2012 through 2016.

RESULTS

Patients who ultimately were diagnosed with NLPHL represented <0.5% of those who underwent FNA+core/CB for an initial suspicion of lymphoma. FNA+core/CB resulted in a definitive diagnosis in 7 of 13 cases, and surgical excisional or incisional biopsy specimens resulted in a definitive diagnosis in 13 of 13 cases (chi-square statistic, 9.6; P = .002). At initial diagnosis, FNA+core/CB was negative in 2 cases and atypical or suspicious in 3 cases; all 5 of those patients required surgical excisional or incisional biopsy for a definitive lymphoma diagnosis. By contrast, patients who underwent FNA+core/CB for recurrent lymphoma required surgical excisional or incisional biopsy in only 1 of 8 cases (chi-square statistic, 9.5; P = .002). Flow cytometry was positive for a light-chain-restricted B-cell population in only 1 of 11 biopsies that were involved by lymphoma.

CONCLUSIONS

Surgical excisional or incisional biopsy remains the gold standard for NLPHL diagnosis and for distinguishing progression to a T-cell/histiocyte-rich large B-cell lymphoma pattern. At a tertiary cancer center with routine collaborative diagnosis of lymphoma on FNA+core/CB by cytopathologists and hematopathologists, FNA+core/CB performs well to assess for recurrent or transformed NLPHL, rarely requiring subsequent surgical excisional or incisional biopsy. FNA+core/CB has limited sensitivity in the initial diagnosis setting.

A rare face of follicular lymphoma: reverse variant of follicular lymphoma

Background

Reverse Variant of Follicular Lymphoma (RVFL) is one of the rare morphological variants of FL, characterized by dark staining small centrocytes in the center and pale staining large centroblasts at the periphery of the neoplastic follicles. Only rare cases of RVFL have been described to date. The histological appearance of this little known variant of FL may be misinterpreted if pathologists are unaware of its existence. The main purpose of this study is to draw pathologists’ attention to such an uncommon growth pattern of FL so that this variant can be correctly recognized and the clinical significance further studied in the future.

Methods

Four cases of FL with unusual morphologic features were evaluated for the expression pattern of CD20, CD10, BCL6, BCL2, CD21, CD23, CD3, CD5, Cyclin D1, IgD and Ki67 by immunohistochemistry. Fluorescence in situ hybridization (FISH) with break-apart probes was performed to detect BCL2 gene rearrangement.

Results

All four cases showed distinctive morphologic pattern of RVFL; in addition, each also exemplified unique morphological features. Immunohistochemical stains confirmed the cells in both the central areas and the peripheral cuffs had the same immunophenotypic profiles, contrasting to the FL with marginal zone differentiation in which only the center of the nodules showed expression of CD10. FISH demonstrated BCL2 gene rearrangement in all cases.

Conclusion

The growth pattern of this rare FL variant may mimic FL with marginal-zone differentiation and other entities including but not limited to marginal zone lymphoma (MZL), progressive transformation of germinal centers (PTGC) and nodular lymphocyte predominant Hodgkin lymphoma (NLPHL). Pathologists should be familiar with this unusual morphological variant to avoid diagnostic pitfalls.

A high number of IgG4-positive plasma cells rules out nodular lymphocyte predominant Hodgkin lymphoma

Nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) is a subtype of Hodgkin lymphoma that frequently shows a nodal growth pattern with abundant reactive B cells in the microenvironment. Early NLPHL cases can be particularly difficult to differentiate from progressively transformed germinal centers (PTGC). Since PTGC have been described to be IgG4 associated in a relatively high proportion of cases, the aim of the present study was to determine if IgG4 immunostaining can be helpful in the differential diagnosis between NLPHL and PTGC. We furthermore aimed to learn if LP cells can express IgG4. For this purpose, 58 cases of PTGC and 56 cases of NLPHL were assessed using IgG4 immunostaining. We could confirm that a significant number of PTGC cases showed high numbers of IgG4-positive plasma cells (22/58, 38%), whereas hot spot areas of IgG4-positive plasma cells were not found in any of the NLPHL cases. In lymph node areas with the differential diagnosis of NLPHL and PTGC, IgG4 immunostaining can therefore provide a helpful diagnostic tool to rule out NLPHL when a high number of IgG4-positive plasma cells are encountered. We also assessed 13 cases with a combination of NLPHL and PTGC in the same lymph node. Five of these cases presented hot spot areas of IgG4-positive plasma cells in the PTGC regions, while no significant numbers of IgG4-positive plasma cells were observed in the NLPHL part of the lymph node. LP cells were never IgG4 positive. Furthermore, immunoglobulin heavy chain rearrangements of single IgG4-positive plasma cells were analyzed, revealing a polyclonal plasma cell population. In summary, our data suggest that IgG4 immunostaining can provide additional information in the diagnostic workup of cases with the differential diagnosis of NLPHL and PTGC. IgG4's inefficiency in clearing antigens may explain why lymph nodes with PTGC are usually strongly enlarged and develop a high number of hyperplastic germinal centers. Polyclonal immunoglobulin heavy chain rearrangements in IgG4-positive plasma cells further support the hypothesis that PTGC represent a misled immune reaction.

Orbital progressive transformation of germinal centers as part of the spectrum of IgG4-related ophthalmic disease: Clinicopathologic features of three cases

Progressive transformation of germinal centers (PTGC) is a form of follicular hyperplasia recently associated with immunoglobulin G4-related disease (IgG4-RD), but the ophthalmic manifestations of this combination are poorly described. In this retrospective case series, we present three cases of IgG4-related orbital disease (IgG4-ROD) showing varying degrees of PTGC involving the orbit and lacrimal gland. Three adult women presented with ill-defined lacrimal gland enlargement. Histologic sections showed variable fibrosis and large, irregular lymphoid follicles with prominent mantle zones penetrating the germinal centers, highlighted by Bcl-2 and/or IgD immunostains. The interfollicular areas contained a mixture of plasma cells, scattered histiocytes and eosinophils. Mixed T and B-cells were present, and no signs of monoclonality were identified. All cases showed more than 100 IgG4 positive cells per high power field. Epstein-Barr virus in situ hybridization performed in one case was negative. The serum IgG4 level was tested in one case and showed elevation above the normal range. After 2–10 months of follow-up, the patients showed either near-complete resolution or no remaining signs of ophthalmic disease. Increasing awareness of these PTGC in extra-nodal locations, including the orbit, may provide a better understanding of the histologic spectrum of this disease.

[Update on nodular lymphocyte predominant Hodgkin's lymphoma and related lesions]

The present article gives an overview of novel developments in the diagnosis of nodular lymphocyte predominant Hodgkin's lymphoma with reference to the revised WHO classification from 2016. Differential diagnoses that are discussed are progressively transformed germinal centers, T cell/histiocyte-rich large B cell lymphoma as well as transformation into a diffuse large B cell lymphoma.

Nodular lymphocyte-predominant Hodgkin lymphoma

Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) is a rare subtype of Hodgkin lymphoma with distinct clinicopathologic features. It is typified by the presence of lymphocyte predominant (LP) cells, which are CD20(+) but CD15(-) and CD30(-) and are found scattered amongst small B lymphocytes arranged in a nodular pattern. Despite frequent and often late or multiple relapses, the prognosis of NLPHL is very favorable. There is an inherent risk of secondary aggressive non-Hodgkin lymphoma (NHL) and studies support that risk is highest in those with splenic involvement at presentation. Given disease rarity, the optimal management is unclear and opinions differ as to whether treatment paradigms should be similar to or differ from those for classical Hodgkin lymphoma (CHL). This review provides an overview of the existing literature describing pathological subtypes, outcome and treatment approaches for NLPHL.

Hodgkin lymphoma: Pathology and biology

The Hodgkin and Reed-Sternberg (HRS) tumor cells of classical Hodgkin lymphoma (HL), as well as the lymphocyte predominant (LP) cells of nodular lymphocyte predominant HL (NLPHL), are derived from mature B cells. However, HRS cells have largely lost their B-cell phenotype and show a very unusual expression of many markers of other hematopoietic cell lineages, which aids in the differential diagnosis between classical HL (cHL) and NLPHL and distinguishes cHL from all other hematopoietic malignancies. The bi- or multinucleated Reed-Sternberg cells most likely derive from the mononuclear Hodgkin cells through a process of incomplete cytokinesis. HRS cells show a deregulated activation of numerous signaling pathways, which is partly mediated by cellular interactions in the lymphoma microenvironment and partly by genetic lesions. In a fraction of cases, Epstein-Barr virus contributes to the pathogenesis of cHL. Recurrent genetic lesions in HRS cells identified so far often involve members of the nuclear factor-κB (NF-κB) and JAK/STAT pathways and genes involved in major histocompatibility complex expression. However, further lead transforming events likely remain to be identified. We here discuss the current knowledge on HL pathology and biology.

Progressive Transformation of Germinal Centers: Single-Center Experience of 33 Turkish Patients

Progressive transformation of germinal centers (PTGCs) is a benign disease of the lymph nodes that is rarely associated with Hodgkin disease. We reviewed the clinical and pathologic features of PTGCs and the relationship of PTGCs with lymphoid neoplasia in an adult population. The data from 33 patients who were diagnosed with PTCGs were retrospectively analyzed. Of the 33 PTGC patients, 48.5% were men and 51.5% were women, with a mean age of 43.8 years at diagnosis. Most of the enlarged and excised lymph nodes were cervical and axillary. Diffuse large B-cell lymphoma and nodular lymphocyte predominant Hodgkin lymphoma was detected concurrent with PTGC in 2 patients. Also, PTGCs was detected 3 years after the diagnosis of diffuse large B-cell lymphoma, nodular lymphocyte predominant Hodgkin lymphoma, and T-cell-rich B-cell lymphoma in 3 patients. No relapse was found in the patients with lymphoma, and no progression to lymphoma was detected during the follow-up of the other patients. PTGCs is not considered a premalignant entity; however, the development of lymphoma has been reported rarely. If PTGCs occurs in the follow-up process of patients with lymphoma, the follow-up intervals should be shortened.