Cellular origins and genetic landscape of cutaneous gamma delta T cell lymphomas

Updated Classification of Cutaneous Lymphoma

The International Consensus Classification (ICC) of myeloid and lymphoid neoplasms follows the precedent set in the Revised European-American lymphoma classification for modern lymphoma classifications by defining specific diseases on the basis of all the available morphologic, immunophenotypic, genetic, and clinical findings. Primary cutaneous lymphomas exhibit a broad range of clinical behavior ranging from lesions which spontaneously regress to those which run an aggressive, often fatal course. Accurate separation of entities is therefore essential for prognostication and to ensure appropriate treatment is administered. However, despite marked differences in clinical course, many subtypes of primary cutaneous lymphoma exhibit remarkably similar, often overlapping, and sometimes indistinguishable pathologic features. While molecular analysis has furthered our understanding of some of these disease entities, it does not yet facilitate robust distinction. Thus, clinical correlation retains a central role in both the diagnosis and classification of primary cutaneous lymphoma. This review aims to draw attention to problem areas in differential diagnosis and hopefully offer some practical suggestions for resolving difficult cases. It will also highlight recent advances in the field and discuss how they reinforce the current classification system and how they might impact of future classifications and treatment strategies.

The fifth edition of the WHO classification of mature T cell, NK cell and stroma-derived neoplasms

The fifth edition of the WHO Classification of Haematolymphoid Tumors (WHO-HAEM5) introduces significant advancements in the understanding and diagnosis of mature T cell and NK cell, and stroma-derived neoplasms, and incorporates molecular and genetic data/findings accrued over the past years. The classification has been reorganised using a hierarchical system, employed across the fifth edition of the WHO classification of tumours of all organ systems. This review highlights recent developments, evolving concepts, and key updates since the revised fourth edition (WHO-HAEM4R). It enumerates the minimal/essential criteria necessary for diagnosis and classification, constituting not only the importance of clonality analysis in the workup of certain T cell neoplasms and the detection of infectious agents and specific genetic alterations in a subset of entities but also the applicability of these criteria in resource-constrained settings. 'Stroma-derived neoplasms of lymphoid tissues discussed in this review is a new category introduced in HAEM5 that encompasses mesenchymal tumours occurring exclusively in lymph nodes and spleen and mesenchymal dendritic cell neoplasms previously classified as 'histiocytic/dendritic cell neoplasms'.

Results from an open-label phase 2a study of cerdulatinib, a dual spleen tyrosine kinase/janus kinase inhibitor, in relapsed/refractory peripheral T-cell lymphoma

In this phase-2a study (NCT01994382), patients aged ≥18 years with relapsed/refractory peripheral T-cell lymphoma (PTCL; angioimmunoblastic T-cell lymphoma/T follicular helper [AITL/TFH], n = 29); PTCL-not otherwise specified [NOS], n = 11; and Other, n = 25) received 30 mg oral cerdulatinib, a reversible dual inhibitor of spleen tyrosine kinase and Janus kinase, twice daily in 28-day cycles until disease progression or unacceptable toxicity. Overall response rate (ORR) was 36.2% (12 complete responses [CR],9 partial responses [PR], and 14 stable disease); median time to response was 1.9 months. ORR was 51.9% for AITL/TFH (10 CR, 4 PR) and 31.8% for Other (2 CR, 5 PR); median duration of response was 12.9 and 5.3 months, respectively. The most common grade ≥3 treatment-emergent adverse events were asymptomatic amylase elevation (23.1%), anemia (20.0%), and asymptomatic lipase elevation (18.5%). These data suggest clinical activity and acceptable tolerability for cerdulatinib in patients with relapsed/refractory PTCL.

Single-cell RNA sequencing comparison of CD4+, CD8+ and T-cell receptor γδ+ cutaneous T-cell lymphomas reveals subset-specific molecular phenotypes

BACKGROUND

Malignant clones of primary cutaneous T-cell lymphomas (CTCL) can show a CD4+, CD8+ or T-cell receptor (TCR)-γδ+ phenotype, but their individual impact on tumour biology and skin lesion formation remains ill defined.

OBJECTIVES

To perform a comprehensive molecular characterization of CD4+ vs. CD8+ and TCR-γδ+ CTCL lesions.

METHODS

We performed single-cell RNA sequencing (scRNAseq) of 18 CTCL skin biopsies to compare classic CD4+ advanced-stage mycosis fungoides (MF) with TCR-γ/δ+ MF and primary cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma (Berti lymphoma).

RESULTS

Malignant clones of TCR-γ/δ+ MF and Bertilymphoma showed similar clustering patterns distinct from CD4+ MF, along with increased expression of cytotoxic markers such as NKG7, CTSW, GZMA and GZMM. Only advanced-stage CD4+ MF clones expressed central memory T-cell markers (SELL, CCR7, LEF1), alongside B1/B2 blood involvement, whereas TCR-γδ+ MF and Berti lymphoma harboured a more tissue-resident phenotype (CD69, CXCR4, NR4A1) without detectable cells in the blood. CD4+ MF and TCR-γδ+ MF skin lesions harboured strong type 2 immune activation across myeloid cells, while Berti lymphoma was more skewed toward type 1 immune responses. Both CD4+ MF and TCR-γδ+ MF lesions showed upregulation of keratinocyte hyperactivation markers such as S100A genes and KRT16. This increase was entirely absent in Berti lymphoma, possibly reflecting an aberrant keratinocyte response to invading tumour cells, which could contribute to the formation of the typical ulceronecrotic lesions within this entity.

CONCLUSIONS

Our scRNAseq profiling study reveals specific molecular patterns associated with distinct CTCL subtypes.

Through thick and thin: confronting the aggressive cutaneous T-cell lymphomas

The cutaneous T-cell lymphomas (CTCLs) comprise a diverse set of diseases with equally diverse presentations ranging from asymptomatic solitary lesions to highly aggressive diseases with propensity for visceral spread. The more aggressive CTCLs, which herein we consider as certain cases of advanced-stage mycosis fungoides/Sézary syndrome (MF/SS), primary cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma (PCAETCL), and primary cutaneous gamma delta T-cell lymphoma (PCGDTCL), require systemic therapy. Over the last 5 years, treatment options for MF/SS have expanded with biological insights leading to new therapeutic options and increasingly unique management strategies. An enhanced appreciation of the compartmental efficacy of these agents (skin, blood, lymph nodes, visceral organs) is incorporated in current management strategies in MF/SS. In addition, approaches that combine modalities in attempts to increase depth and durability of responses across multiple compartments are being trialed. In contrast to MF/SS, PCAETCL and PCGDTCL remain diseases with few prospective studies to guide treatment. However, recent genomic insights on these diseases, such as the presence of JAK2 fusions in PCAETCL and cell of origin findings in PCGDTCL, have created options for new biomarker-driven strategies.

Distinctive genomic features of human T-lymphotropic virus type 1-related adult T-cell leukemia-lymphoma in Western populations

Adult T-cell leukemia-lymphoma (ATLL) is an aggressive malignancy driven by human T-cell leukemia virus type 1 (HTLV-1). Although patients from the Western hemisphere (Afro-Caribbean and South American) face worse prognoses, our understanding of ATLL molecular drivers derives mostly from Japanese studies. We performed multi-omic analyses to elucidate the genomic landscape of ATLL in Western cohorts. Recurrent deletions and/or damaging mutations involving FOXO3, ANKRD11, DGKZ, and PTPN6 implicate these genes as potential tumor suppressors. RNA-sequencing, published functional data and in vitro assays support the roles of ANKRD11 and FOXO3 as regulators of T-cell proliferation and apoptosis in ATLL, respectively. Survival data suggest that ANKRD11 mutation may confer a worse prognosis. Japanese and Western cohorts, in addition to acute and lymphomatous subtypes, demonstrated distinct molecular patterns. GATA3 deletion was associated with chronic cases with unfavorable outcomes. IRF4 and CARD11 mutations frequently emerged in relapses after interferon therapy. Our findings reveal novel putative ATLL driver genes and clinically relevant differences between Japanese and Western ATLL patients.

Rapidly Progressive Primary Cutaneous Gamma Delta T-Cell Lymphoma With FYN Gene Alteration

ABSTRACT

Primary cutaneous gamma delta T-cell lymphoma (PCGDTCL) is a rare type of non-Hodgkin lymphoma accounting for <1% of primary cutaneous T-cell lymphomas. The exact cause of PCGDTCL is not known, however, it is thought that chronic antigen exposure in the skin may lead to immune dysregulation at the site, resulting in abnormal proliferation of mature, post-thymic cytotoxic gamma delta T cells. Mutations are the most common genetic alteration seen in PCGDTCL, while structural abnormalities such as gene fusions are not common. We report a case of PCGDTCL with atypical immunophenotypic features, including expression of CD5 with lack of cytotoxic marker expression, and a structural alteration leading to FYN deletion at exon 8. Recently, it was described that a deletion of the area between FYN exon 8 and TRAF3IP2 intron 2 results in a novel FYN::TRAF3IP2 fusion in peripheral T-cell lymphoma, not otherwise specified. We describe our patient's clinical course, differential diagnosis, and potential implications of FYN deletion on disease pathogenesis. To our knowledge, this is the first report of an FYN structural alteration to be described in PCGDTCL.

Preexisting Skin-Resident CD8 and γδ T-cell Circuits Mediate Immune Response in Merkel Cell Carcinoma and Predict Immunotherapy Efficacy

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin cancer with a ∼50% response rate to immune checkpoint blockade (ICB) therapy. To identify predictive biomarkers, we integrated bulk and single-cell RNA sequencing (RNA-seq) with spatial transcriptomics from a cohort of 186 samples from 116 patients, including bulk RNA-seq from 14 matched pairs pre- and post-ICB. In nonresponders, tumors show evidence of increased tumor proliferation, neuronal stem cell markers, and IL1. Responders have increased type I/II interferons and preexisting tissue resident (Trm) CD8 or Vδ1 γδ T cells that functionally converge with overlapping antigen-specific transcriptional programs and clonal expansion of public T-cell receptors. Spatial transcriptomics demonstrated colocalization of T cells with B and dendritic cells, which supply chemokines and costimulation. Lastly, ICB significantly increased clonal expansion or recruitment of Trm and Vδ1 cells in tumors specifically in responders, underscoring their therapeutic importance. These data identify potential clinically actionable biomarkers and therapeutic targets for MCC. Significance: MCC serves as a model of ICB response. We utilized the largest-to-date, multimodal MCC dataset (n = 116 patients) to uncover unique tumor-intrinsic properties and immune circuits that predict response. We identified CD8 Trm and Vδ1 T cells as clinically actionable mediators of ICB response in major histocompatibility complex-high and -low MCCs, respectively.

Fifth Edition of the World Health Organization Classification of Tumors of the Hematopoietic and Lymphoid Tissues: Mature T-Cell, NK-Cell, and Stroma-Derived Neoplasms of Lymphoid Tissues

This review focuses on mature T cells, natural killer (NK) cells, and stroma-derived neoplasms in the fifth edition of the World Health Organization classification of hematolymphoid tumors, including changes from the revised fourth edition. Overall, information has expanded, primarily due to advancements in genomic understanding. The updated classification adopts a hierarchical format. The updated classification relies on a multidisciplinary approach, incorporating insights from a diverse group of pathologists, clinicians, and geneticists. Indolent NK-cell lymphoproliferative disorder of the gastrointestinal tract, Epstein-Barr virus-positive nodal T- and NK-cell lymphoma, and several stroma-derived neoplasms of lymphoid tissues have been newly introduced or included. The review also provides guidance on how the fifth edition of the World Health Organization classification of hematolymphoid tumors can be applied in routine clinical practice.

Classifications of cutaneous lymphomas and lymphoproliferative disorders: An update from the EORTC cutaneous lymphoma histopathology group

The classification of primary cutaneous lymphomas and lymphoproliferative disorders (LPD) is continuously evolving by integrating novel clinical, pathological and molecular data. Recently two new classifications for haematological malignancies including entities of cutaneous lymphomas were proposed: the 5th edition of the WHO classification of haematolymphoid tumours and the International Consensus Classification (ICC) of mature lymphoid neoplasms. This article provides an overview of the changes introduced in these two classifications compared to the previous WHO classification. The main changes shared by both classifications include the downgrading of CD8+ acral T-cell lymphoma to CD8+ acral T-cell LPD, and the recognition of entities that were previously categorized as provisional and have now been designated as definite types including primary cutaneous small or medium CD4+ T-cell LPD, primary cutaneous gamma/delta T-cell lymphoma, primary cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma, Epstein-Barr virus-positive mucocutaneous ulcer. Both classifications consider primary cutaneous marginal zone B-cell clonal neoplasm as an indolent disease but use a different terminology: primary cutaneous marginal zone lymphoma (WHO) and primary cutaneous marginal zone LPD (ICC). The 5th WHO classification further introduces and provides essential and desirable diagnostic criteria for each disease type and includes chapters on reactive B- or T-cell rich lymphoid proliferations formerly referred as cutaneous pseudolymphomas, as well as histiocyte and CD8 T-cell rich LPD in patients with inborn error of immunity. As already emphasized in previous lymphoma classifications, the importance of integrating clinical, histological, phenotypic and molecular features remains the crucial conceptual base for defining cutaneous (and extracutaneous) lymphomas.

Atypical presentation of γ/δ mycosis fungoides with an unusual phenotype and SOCS1 mutation

Mycosis fungoides is the most frequent subtype of primary cutaneous T-cell lymphomas. The diagnosis is based on a thorough clinic-pathologic correlation, which can, especially in early-stage disease, be challenging due to similarities with several benign skin disorders such as psoriasis and atopic dermatitis. Here, we present a case of an 81-year-old man with a 20-year-long medical history of skin problems treated as psoriasis with limited effect. Since December 2021, the patient experienced worsening of his skin symptoms with rapidly growing tumors and widespread patches and plaques. Positron emission tomography/computed tomography evaluation revealed markedly metabolic activity related to the skin tumors and increased FDG uptake in several retroperitoneal lymph nodes. Histological assessment of skin biopsies demonstrated a highly proliferative T-cell lymphoma with a γ/δ+ and CD8+ cytotoxic phenotype. The morphology of the tumor cells appeared blastic with an abnormal immunephenotype CD3+, CD2-, CD5dim, CD4-, CD8+, CD56-, and CD30-. Next-generation sequencing detected a likely pathogenic SOCS1 mutation with an allele frequency of 72% as well as a STAT3 variant of unknown significance. This case highlights the diagnostic complexity of an indolent skin lymphoma evolving into an aggressive cytotoxic lymphoma.

Primary Cutaneous Peripheral T-Cell Lymphoma NOS: Diagnostic Criteria and Challenges

ABSTRACT

Primary cutaneous peripheral T-cell lymphoma not otherwise specified (PTCL NOS) denotes lymphomas that do not conform to a recognized entity. Within this category, 3 specific lymphoproliferative diseases had been granted provisional status pending further confirmation of their validity as distinct entities; acral CD8+ lymphoma-recently accepted as acral CD8+ lymphoproliferative disorder-aggressive epidermotropic CD8+ cytotoxic T-cell lymphoma, and CD4+ small-medium T-cell lymphoproliferative disorder. The adoption of stringent diagnostic criteria, which include clinical, morphological, and immunohistochemical data, and some inherent variations of these within individual cases, raises problems as to the boundaries between these tumors and a diagnosis of PTCL NOS. This review discusses the evolution of our knowledge of these tumors and their diagnostic criteria with respect to the wider PTCL NOS category.

Update on primary cutaneous T-cell lymphomas rare subtypes

Rare subtypes of cutaneous T-cell lymphomas (CTCL) include four entities, primary cutaneous γδ T-cell lymphoma, primary cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma, and primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorders, primary cutaneous acral CD8+ T-cell lymphoma, which were previously considered provisional and are now included in the new 5th World Health Organization classification of hematolymphoid tumors as distinct entities. An updated summary of the clinical, histological, and genomic characteristics of these uncommon CTCL subtypes is given in this review, with a focus on the growing body of knowledge regarding their classification and possible treatment strategies.

Lymphomatoid Papulosis With T-cell Receptor-Gamma Delta Expression: A Clinicopathologic Case-series of 26 Patients of an Underrecognized Immunophenotypic Variant of Lymphomatoid Papulosis

Lymphomatoid papulosis (LyP) has several histopathologic presentations. LyP featuring gamma-delta (γδ) T-cell receptor expression may masquerade as and may be misdiagnosed as aggressive cutaneous T-cell lymphoma, particularly primary cutaneous γδ T-cell lymphoma (PCGDTL) or γδ mycosis fungoides. We performed a clinicopathologic analysis of the largest series of LyP featuring γδ T-cell expression. We identified 26 patients with a diagnosis of LyP with γδ T cells from our institutions, as well as through a comprehensive review of the literature, and characterized these cases. Most cases were treated with topical steroids or not treated at all. The majority of cases showed a CD4 - CD8 + phenotype and featured at least one cytotoxic marker. Histopathologic features included an intraepidermal or dermal infiltrate with large cells and frequent angiotropism. One case was initially misdiagnosed as PCGDTL, requiring further therapy. Our case series, the largest international cohort of γδ T cell predominant LyP cases, confirms marked clinicopathologic heterogeneity that may contribute to misdiagnosis, reasserting the need to identify classic clinical features, CD30 + T-cell components, and markers of cytotoxicity when dealing with this differential diagnosis. A limitation of this study includes somewhat limited follow-up, histologic, and immunophenotypic information for some cases.

Pediatric cutaneous T-cell neoplasm and mimics with gamma-delta expression: Not always aggressive

Pediatric cutaneous T-cell lymphoma with γδ immunophenotype is extremely rare. Only a few cases of γδ T-cell neoplasm have been reported in the literature, and therefore little is known whether γδ T-cell neoplasms in children are distinct from their adult counterparts with respect to the clinicopathological presentation, behavior, and prognosis. In this study, we demonstrate three unique pediatric cutaneous T-cell neoplasm and mimics with increased γδ T cells. All cases showed an indolent clinical course.

Naturally occurring T cell mutations enhance engineered T cell therapies

Adoptive T cell therapies have produced exceptional responses in a subset of patients with cancer. However, therapeutic efficacy can be hindered by poor T cell persistence and function1. In human T cell cancers, evolution of the disease positively selects for mutations that improve fitness of T cells in challenging situations analogous to those faced by therapeutic T cells. Therefore, we reasoned that these mutations could be co-opted to improve T cell therapies. Here we systematically screened the effects of 71 mutations from T cell neoplasms on T cell signalling, cytokine production and in vivo persistence in tumours. We identify a gene fusion, CARD11-PIK3R3, found in a CD4+ cutaneous T cell lymphoma2, that augments CARD11-BCL10-MALT1 complex signalling and anti-tumour efficacy of therapeutic T cells in several immunotherapy-refractory models in an antigen-dependent manner. Underscoring its potential to be deployed safely, CARD11-PIK3R3-expressing cells were followed up to 418 days after T cell transfer in vivo without evidence of malignant transformation. Collectively, our results indicate that exploiting naturally occurring mutations represents a promising approach to explore the extremes of T cell biology and discover how solutions derived from evolution of malignant T cells can improve a broad range of T cell therapies.

Descriptive Analysis and Factors Influencing Survival in Patients With Primary Cutaneous Gamma-Delta T Cell Lymphoma. A Retrospective National Cancer Database Study

BACKGROUND

Gamma delta T cells gives rise to a rare malignancy called Primary cutaneous Gamma-Delta T cell lymphoma (PCGDTCL).

METHODS

From the National Cancer Database (NCDB), 110 (0.015%) patients with PCGDTCL were identified.

RESULTS

Males aged >60 years were the commonest cohort. Caucasian race was the most common (Caucasian: 79.09%, African American:16.36%). Most patients were diagnosed at stage 1 (52.33%), followed by stage 4 (30.23%). On analyzing income categories, <$48,000 group had 48.15% stage 4 (13/27) and 40.74% (11/27) stage 1. Overall survival (OS) of the study group at 3 years by Kaplan-Meier (KM) analysis was 46.6%. African American race (37.5%), income of <$48,000 (27.6%) and government insurance (38.8%) had lower survival rates in KM analysis. In the adjusted hazard ratio (HR) analysis, only age <=40 years compared to >60 years (0.165 [0.036, 0.768], P= .0217) reached significance. Although the group that did not receive any chemotherapy or radiation seemed to have a better survival by KM analysis at 74.3% at 3 years, significance was not seen in the adjusted HR estimates and majority of the patients in this group were stage 1. This group may have received topical treatments which may have not been captured in NCDB. Adjusted analysis also revealed chemoradiation to have a lower mortality risk compared to chemotherapy alone (0.229 [0.079, 0.670], P = .0071), suggesting that aggressive strategies may be required for management when needed.

CONCLUSION

Socioeconomic disparities significantly impact access to healthcare and are of particular importance in rare lymphomas.

DUSP22-IRF4 Rearranged CD30-Positive Primary Cutaneous Lymphoproliferative Disorder With Gamma/Delta Phenotype

ABSTRACT

CD30-positive primary cutaneous lymphoproliferative disorders (CD30 + PCLPD) are a heterogeneous group of cutaneous T-cell lymphoma (CTCL) that includes lymphomatoid papulosis (LyP) and primary cutaneous anaplastic large cell lymphoma. They exist as a clinical and pathological spectrum, which display significant overlap and variability. The diagnosis is made based on correlation between clinical and histopathologic findings. LyP with 6p25.3 rearrangement subtype represents <5% of LyP cases and is defined by DUSP22-IRF4 rearrangement on 6p25.3 locus. The reported cases express the alpha/beta T-cell receptor and follow an indolent clinical behavior typical of LyP. The same rearrangement is detected in 28% of anaplastic large cell lymphoma. We hereby present an extraordinary case of CD30 + PCLPD with DUSP22-IRF4 rearrangement and novel expression of gamma/delta T-cell immunophenotype in a young patient. Although the gamma/delta T-cell immunophenotype has been described in many other T-cell lymphomas, this is the first reported association with CD30 + PCLPD with DUSP22-IRF4 rearrangement.

A Rare Case of Primary Cutaneous Gamma-Delta T-cell Lymphoma with Aberrant B-cell Marker Expression

ABSTRACT

Primary cutaneous gamma-delta T-cell lymphoma (PCGDTL) is a rare and diagnostically challenging primary skin lymphoma. We present a case of a 78-year-old otherwise healthy man who developed nonhealing nodules on his right posterior calf. Initial biopsy showed a dense, atypical, lymphoid infiltrate with gamma-delta and cytotoxic T-cell immunophenotypes. The diagnosis of PCGDTL was rendered; however, concurrent flow cytometry revealed expression of aberrant B-cell markers, including CD19 and cytoplasmic CD79a. Subsequent immunohistochemical studies corroborated this result. We report the extremely rare phenomenon of aberrant B-cell marker expression in PCGDTL, the first formally reported case to our knowledge.

Primary cutaneous T-cell lymphoma: a review of the most common entities with focus on recent updates

Cutaneous T-cell lymphomas are an heterogeneous group of uncommon lymphoid neoplasms that are challenging to diagnose and require close collaboration between dermatologists, pathologists and hematologists/oncologists. This article reviews the most common cutaneous T-cell lymphomas: mycosis fungoides (both classic and variant forms) as well as its leukemic counterpart Sézary syndrome, CD30+ T-cell lymphoproliferative disorders including the ever-expanding group of lymphomatoid papulosis and primary cutaneous anaplastic large cell lymphoma, and primary cutaneous CD4+ small/medium lymphoproliferative disorder. We discuss the classic clinical and histopathologic features of these lymphomas and review how they can be distinguished from reactive entities. In particularly, updates to these diagnostic categories and current controversies in classification are highlighted. Moreover, we review the prognosis and treatment for each entity. These lymphomas exhibit variable prognosis, and therefore it is important to correctly classify atypical cutaneous T-cell infiltrates for appropriate patient treatment and prognosis. Cutaneous T-cell lymphomas are at the interface of several medical specialties; this review seeks to summarize key features of these lymphomas and highlight new and emerging insights into these lymphomas.

PD-1 instructs a tumor-suppressive metabolic program that restricts glycolysis and restrains AP-1 activity in T cell lymphoma

The PDCD1-encoded immune checkpoint receptor PD-1 is a key tumor suppressor in T cells that is recurrently inactivated in T cell non-Hodgkin lymphomas (T-NHLs). The highest frequencies of PDCD1 deletions are detected in advanced disease, predicting inferior prognosis. However, the tumor-suppressive mechanisms of PD-1 signaling remain unknown. Here, using tractable mouse models for T-NHL and primary patient samples, we demonstrate that PD-1 signaling suppresses T cell malignancy by restricting glycolytic energy and acetyl coenzyme A (CoA) production. In addition, PD-1 inactivation enforces ATP citrate lyase (ACLY) activity, which generates extramitochondrial acetyl-CoA for histone acetylation to enable hyperactivity of activating protein 1 (AP-1) transcription factors. Conversely, pharmacological ACLY inhibition impedes aberrant AP-1 signaling in PD-1-deficient T-NHLs and is toxic to these cancers. Our data uncover genotype-specific vulnerabilities in PDCD1-mutated T-NHL and identify PD-1 as regulator of AP-1 activity.

SOHO State of the Art Updates and Next Questions | Challenging Cases in Rare T-Cell Lymphomas

Mature T- and NK-cell neoplasms (MTNKN) collectively represent a rare disorder, representing less than 15% of all non-Hodgkin lymphoma (NHL) cases and qualifying for orphan disease designation by the U.S. Food and Drug Administration (FDA). These consist of 9 families in the fifth revised WHO classification of lymphoid neoplasms, which are made up of over 30 disease subtypes, underscoring the heterogeneity of clinical features, molecular biology, and genetics across this disease group. Moreover, the 5 most common subtypes (peripheral T-cell lymphoma, not otherwise specified; nodal TFH cell lymphoma, angioimmunoblastic type; extranodal NK-cell/T-cell lymphoma; adult T-cell leukemia/lymphoma; and ALK-positive or -negative anaplastic large cell lymphoma) comprise over 75% of MTNKN cases, so other subtypes are exceedingly rare in the context of all NHL diagnoses and consequently often lack consensus on best practices in diagnosis and management. In this review, we discuss the following entities-enteropathy-associated T-cell lymphoma (EATL), monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL), hepatosplenic T-cell lymphoma (HSTCL), subcutaneous panniculitis-like T-cell lymphoma (SPTCL), and primary cutaneous ɣδ T-cell lymphoma (PCGD-TCL) - with an emphasis on clinical and diagnostic features and options for management.

The genesis of human hematopoietic stem cells

Developmental hematopoiesis consists of multiple, partially overlapping hematopoietic waves that generate the differentiated blood cells required for embryonic development while establishing a pool of undifferentiated hematopoietic stem cells (HSCs) for postnatal life. This multilayered design in which active hematopoiesis migrates through diverse extra and intraembryonic tissues has made it difficult to define a roadmap for generating HSCs vs non-self-renewing progenitors, especially in humans. Recent single-cell studies have helped in identifying the rare human HSCs at stages when functional assays are unsuitable for distinguishing them from progenitors. This approach has made it possible to track the origin of human HSCs to the unique type of arterial endothelium in the aorta-gonad-mesonephros region and document novel benchmarks for HSC migration and maturation in the conceptus. These studies have delivered new insights into the intricate process of HSC generation and provided tools to inform the in vitro efforts to replicate the physiological developmental journey from pluripotent stem cells via distinct mesodermal and endothelial intermediates to HSCs.

Primary cutaneous T-cell lymphoma: a review of the most common entities with focus on recent updates

Cutaneous T-cell lymphomas are an heterogeneous group of uncommon lymphoid neoplasms that are challenging to diagnose and require close collaboration between dermatologists, pathologists and hematologists/oncologists. This article reviews the most common cutaneous T-cell lymphomas: mycosis fungoides (both classic and variant forms) as well as its leukemic counterpart Sézary syndrome, CD30+ T-cell lymphoproliferative disorders including the ever-expanding group of lymphomatoid papulosis and primary cutaneous anaplastic large cell lymphoma, and primary cutaneous CD4+ small/medium lymphoproliferative disorder. We discuss the classic clinical and histopathologic features of these lymphomas and review how they can be distinguished from reactive entities. In particularly, updates to these diagnostic categories and current controversies in classification are highlighted. Moreover, we review the prognosis and treatment for each entity. These lymphomas exhibit variable prognosis, and therefore it is important to correctly classify atypical cutaneous T-cell infiltrates for appropriate patient treatment and prognosis. Cutaneous T-cell lymphomas are at the interface of several medical specialties; this review seeks to summarize key features of these lymphomas and highlight new and emerging insights into these lymphomas.

Coexpression of natural killer cell antigens by T-cell large granular lymphocytes in hydroa vacciniforme lymphoproliferative disorder and the involvement of Vδ1 + epithelial-type γδT cells

Hydroa vacciniforme lymphoproliferative disorder (HV-LPD) is a cutaneous variant of chronic active Epstein-Barr virus disease. We examined the coexpression of T- and natural killer (NK)-cell antigens in five patients with classic HV (cHV) and five with systemic HV (sHV). T-cell receptor (TCR) repertoire analysis was performed with high‑throughput sequencing. All five cHV patients had increased γδT cells (> 5%), whereas five sHV patients showed γδT- and αβT-cell dominance in two patients each, and a mixture of abnormal γδT and αβT cells in one. Circulating CD3 + T cells expressed CD16/CD56 at 7.8-42.3% and 1.1-9.7% in sHV and cHV, respectively. The percentage of CD16/CD56 + T cells was higher in the large granular lymphocyte or atypical T-cell fractions in sHV, but no TCR Vα24 invariant chain characteristic of NKT cells was detected. Considerable numbers of CD3 + cells expressing CD56 were observed in sHV skin infiltrates. Of the circulating γδT cells tested, TCR Vδ1 + cells characteristic of the epithelial type of γδT cells were dominant in two sHV cases. Thus, atypical αβT and γδT cells in HV-LPD can express NK-cell antigens, such as CD16 and CD56, and Vδ1 + epithelial-type γδT cells are a major cell type in some HV-LPD cases.

An update on genetic aberrations in T-cell neoplasms

T-cell neoplasms are a highly heterogeneous group of leukaemias and lymphomas that represent 10-15% of all lymphoid neoplasms. Traditionally, our understanding of T-cell leukaemias and lymphomas has lagged behind that of B-cell neoplasms, in part due to their rarity. However, recent advances in our understanding of T-cell differentiation, based on gene expression and mutation profiling and other high throughput methods, have better elucidated the pathogenetic mechanisms of T-cell leukaemias and lymphomas. In this review, we provide an overview of many of the molecular abnormalities that occur in various types of T-cell leukaemia and lymphoma. Much of this knowledge has been used to refine diagnostic criteria that has been included in the fifth edition of the World Health Organization. This knowledge is also being used to improve prognostication and identify novel therapeutic targets, and we expect this progress will continue, eventually resulting in improved outcomes for patients with T-cell leukaemias and lymphomas.

Aggressive Cutaneous Lymphomas and Their Mimics

Cutaneous lymphomas encompass a heterogeneous group of neoplasms with a wide spectrum of clinical presentations, histopathologic features, and prognosis. Because there are overlapping pathologic features among indolent and aggressive forms and with systemic lymphomas that involve the skin, clinicopathologic correlation is essential. Herein, the clinical and histopathologic features of aggressive cutaneous B- and T-cell lymphomas are reviewed. Indolent cutaneous lymphomas/lymphoproliferative disorders, systemic lymphomas, and reactive processes that may mimic these entities are also discussed. This article highlights distinctive clinical and histopathologic features, increases awareness of rare entities, and presents new and evolving developments in the field.

Primary Cutaneous Gamma-Delta T-cell Lymphoma: A Case Report and Review of Literature

Primary cutaneous gamma-delta T-cell lymphoma (PCGD-TCL) is a rare type of lymphoma, representing less than 1% of all cutaneous T-cell lymphomas. It is typically aggressive and chemotherapy-refractory. Hence, most institutions tend to employ intensive chemotherapy followed by stem cell transplantation although there is no standard of care established. We report a case of PCGD-TCL and discuss the challenges associated with the diagnosis and management of PCGD-TCL.

Emerging predictive biomarkers for novel therapeutics in peripheral T-cell and natural killer/T-cell lymphoma

Peripheral T-cell lymphoma (PTCL) and natural killer/T-cell lymphoma (NKTCL) are rare subtypes of non-Hodgkin's lymphoma that are typically associated with poor treatment outcomes. Contemporary first-line treatment strategies generally involve the use of combination chemoimmunotherapy, radiation and/or stem cell transplant. Salvage options incorporate a number of novel agents including epigenetic therapies (e.g. HDAC inhibitors, DNMT inhibitors) as well as immune checkpoint inhibitors. However, validated biomarkers to select patients for individualized precision therapy are presently lacking, resulting in high treatment failure rates, unnecessary exposure to drug toxicities, and missed treatment opportunities. Recent advances in research on the tumor and microenvironmental factors of PTCL and NKTCL, including alterations in specific molecular features and immune signatures, have improved our understanding of these diseases, though several issues continue to impede progress in clinical translation. In this Review, we summarize the progress and development of the current predictive biomarker landscape, highlight potential knowledge gaps, and discuss the implications on novel therapeutics development in PTCL and NKTCL.

Surfing on the waves of the human γδ T cell ontogenic sea

While γδ T cells are present virtually in all vertebrates, there is a remarkable lack of conservation of the TRG and TRD loci underlying the generation of the γδ T cell receptor (TCR), which is associated with the generation of species-specific γδ T cells. A prominent example is the human phosphoantigen-reactive Vγ9Vδ2 T cell subset that is absent in mice. Murine γδ thymocyte cells were among the first immune cells identified to follow a wave-based layered development during embryonic and early life, and since this initial observation, in-depth insight has been obtained in their thymic ontogeny. By contrast, less is known about the development of human γδ T cells, especially regarding the generation of γδ thymocyte waves. Here, after providing an overview of thymic γδ wave generation in several vertebrate classes, we review the evidence for γδ waves in the human fetal thymus, where single-cell technologies have allowed the breakdown of human γδ thymocytes into functional waves with important TCR associations. Finally, we discuss the possible mechanisms contributing to the generation of waves of γδ thymocytes and their possible significance in the periphery.

Recent advances in cutaneous lymphoma-implications for current and future classifications

The Revised European-American Classification of mature lymphoid neoplasms published in 1994 and the 2001, 2008 and 2016 WHO classifications that followed, were the product of international collaboration and consensus amongst haematopathologists, geneticists, molecular scientists and clinicians. Primary cutaneous lymphomas were fully incorporated into this process following the publication of the WHO-EORTC classification of cutaneous lymphomas in 2005. The definition, diagnostic criteria and recommended studies for primary cutaneous lymphoma continue to be refined. The 2022 International Consensus Classification represents the most recent update and an overview of all the main entities presenting primarily in the skin, together with the major changes in classification, are summarized herein. Primary cutaneous marginal zone lymphoma is segregated from other extranodal marginal zone lymphomas of mucosa-associated lymphoid tissue (MALT lymphoma) and downgraded to a lymphoproliferative disorder in line with its markedly indolent behaviour. In addition, two subtypes are recognised, based largely but not exclusively on whether they are heavy chain class-switched or IgM positive. Similarly, in keeping with a trend to greater conservatism, primary cutaneous acral CD8 positive T cell lymphoma is now also classified as a lymphoproliferative disorder. In addition, significant new insights into the biology of primary cutaneous lymphoma have also recently been forthcoming and will be presented. These studies have enhanced our knowledge of genetic, epigenetic and transcriptional changes in this group of diseases. They not only identify potential targets for novel therapies, but also raise as yet unanswered questions as to how we categorise cutaneous lymphomas, particularly with respect to relationships with similar lymphomas at extracutaneous sites.

Primary cutaneous gamma-delta T-cell lymphoma masquerading as leukemia cutis in a patient recently diagnosed with small lymphocytic lymphoma: Clues to the diagnosis

A 54-year-old man recently diagnosed with small lymphocytic lymphoma (SLL) had waxing and waning, indurated, erythematous plaques on his legs, with leukopenia and anemia disproportionate to the SLL burden in his marrow and pelvic lymph nodes. Punch biopsy of a plaque performed to evaluate for leukemia cutis revealed a lymphocytic lobular-panniculitis-like infiltrate resembling lupus panniculitis, but a preponderance of CD8+/Ki-67+ T-cells surrounding adipocytes raised concern for subcutaneous panniculitis-like T-cell lymphoma (SPTCL). Additional immunohistochemistry (IHC) studies showed that the adipotropic T-cells expressed TCR-gamma, supporting the rare, unexpected diagnosis of Primary cutaneous gamma-delta T-cell lymphoma (PCGDTCL). The patient subsequently met diagnostic criteria for hemophagocytic lymphohistiocytosis (HLH). PCGDTCL is an aggressive, HLH-associated lymphoma requiring different management than SPTCL and SLL. This case illustrates how PCGDTCL can co-exist with B-cell lymphoma and resemble panniculitis on biopsies. PCGDTCL and SPTCL should enter the differential diagnosis whenever patients present with the constellation of lobular panniculitis and unexplained cytopenias. In the present case, close clinicopathologic correlation and judicious use of IHC on a small sample allowed for a prompt diagnosis.

Advances in the understanding and treatment of Cutaneous T-cell Lymphoma

Cutaneous T-cell lymphomas (CTCL) are a heterogeneous group of non-Hodgkin's lymphomas (NHL) characterised by the clonal proliferation of malignant, skin homing T-cells. Recent advances have been made in understanding the molecular pathogenesis of CTCL. Multiple deep sequencing studies have revealed a complex genomic landscape with large numbers of novel single nucleotide variants (SNVs) and copy number variations (CNVs). Commonly perturbed genes include those involved in T-cell receptor signalling, T-cell proliferation, differentiation and survival, epigenetic regulators as well as genes involved in genome maintenance and DNA repair. In addition, studies in CTCL have identified a dominant UV mutational signature in contrast to systemic T-cell lymphomas and this likely contributes to the high tumour mutational burden. As current treatment options for advanced stages of CTCL are associated with short-lived responses, targeting these deregulated pathways could provide novel therapeutic approaches for patients. In this review article we summarise the key pathways disrupted in CTCL and discuss the potential therapeutic implications of these findings.

Development of γδ T cells in the thymus - A human perspective

γδ T cells are increasingly emerging as crucial immune regulators that can take on innate and adaptive roles in the defence against pathogens. Although they arise within the thymus from the same hematopoietic precursors as conventional αβ T cells, the development of γδ T cells is less well understood. In this review, we focus on summarising the current state of knowledge about the cellular and molecular processes involved in the generation of γδ T cells in human.

Genetics Abnormalities with Clinical Impact in Primary Cutaneous Lymphomas

Simple Summary

The genetic landscape of cutaneous T-cell lymphomas analyzed by sequencing high throughput techniques shows a heterogeneous somatic mutational profile and genomic copy number variations in the TCR signaling effectors, the NF-κB elements, DNA damage/repair elements, JAK/STAT pathway elements and epigenetic modifiers. A mutational and genomic stratification of these patients provides new opportunities for the development or repurposing of (personalized) therapeutic strategies. The genetic heterogeneity in cutaneous B-cell lymphoma parallels with the specific subtype. Damaging mutations in primary cutaneous diffuse large B-cell lymphoma of the leg type, involving MYD88 gene, or BCL6 and MYC translocations or CDKN2A deletions are useful for diagnostic purposes. The more indolent forms, as the primary cutaneous lymphoma of follicle center cell (somatic mutations in TNFRSF14 and 1p36 deletions) and the cutaneous lymphoproliferative disorder of the marginal zone cells (FAS gene), present with a more restricted pattern of genetic alterations.

Abstract

Primary cutaneous lymphomas comprise a heterogeneous group of extranodal non-Hodgkin lymphomas (NHL) that arise from skin resident lymphoid cells and are manifested by specific lymphomatous cutaneous lesions with no evidence of extracutaneous disease at the time of diagnosis. They may originate from mature T-lymphocytes (70% of all cases), mature B-lymphocytes (25–30%) or, rarely, NK cells. Cutaneous T-cell lymphomas (CTCL) comprise a heterogeneous group of T-cell malignancies including Mycosis Fungoides (MF) the most frequent subtype, accounting for approximately half of CTCL, and Sézary syndrome (SS), which is an erythrodermic and leukemic subtype characterized by significant blood involvement. The mutational landscape of MF and SS by NGS include recurrent genomic alterations in the TCR signaling effectors (i.e., PLCG1), the NF-κB elements (i.e., CARD11), DNA damage/repair elements (TP53 or ATM), JAK/STAT pathway elements or epigenetic modifiers (DNMT3). Genomic copy number variations appeared to be more prevalent than somatic mutations. Other CTCL subtypes such as primary cutaneous anaplastic large cell lymphoma also harbor genetic alterations of the JAK/STAT pathway in up to 50% of cases. Recently, primary cutaneous aggressive epidermotropic T-cell lymphoma, a rare fatal subtype, was found to contain a specific profile of JAK2 rearrangements. Other aggressive cytotoxic CTCL (primary cutaneous γδ T-cell lymphomas) also show genetic alterations in the JAK/STAT pathway in a large proportion of patients. Thus, CTCL patients have a heterogeneous genetic/transcriptional and epigenetic background, and there is no uniform treatment for these patients. In this scenario, a pathway-based personalized management is required. Cutaneous B-cell lymphoma (CBCL) subtypes present a variable genetic profile. The genetic heterogeneity parallels the multiple types of specialized B-cells and their specific tissue distribution. Particularly, many recurrent hotspot and damaging mutations in primary cutaneous diffuse large B-cell lymphoma of the leg type, involving MYD88 gene, or BCL6 and MYC translocations and BLIMP1 or CDKN2A deletions are useful for diagnostic and prognostic purposes for this aggressive subtype from other indolent CBCL forms.

Comparing Mouse and Human Tissue-Resident γδ T Cells

Circulating immune cell compartments have been extensively studied for decades, but limited access to peripheral tissue and cell yield have hampered our understanding of tissue-based immunity, especially in γδ T cells. γδ T cells are a unique subset of T cells that are rare in secondary lymphoid organs, but enriched in many peripheral tissues including the skin, uterus, and other epithelial tissues. In addition to immune surveillance activities, recent reports have revealed exciting new roles for γδ T cells in homeostatic tissue physiology in mice and humans. It is therefore important to investigate to what extent the developmental rules described using mouse models transfer to human γδ T cells. Besides, it will be necessary to understand the differences in the development and biogenesis of human and mouse γδ T cells; to understand how γδ T cells are maintained in physiological and pathological circumstances within different tissues, as well as characterize the progenitors of different tissue-resident γδ T cells. Here, we summarize current knowledge of the γδ T phenotype in various tissues in mice and humans, describing the similarities and differences of tissue-resident γδ T cells in mice and humans.

Single-Cell RNA Sequencing Unveils the Clonal and Transcriptional Landscape of Cutaneous T-Cell Lymphomas

PURPOSE

Clonal malignant T lymphocytes constitute only a fraction of T cells in mycosis fungoides skin tumors and in the leukemic blood of Sézary syndrome, the classic types of cutaneous T-cell lymphomas. However, lack of markers specific for malignant lymphocytes prevents distinguishing them from benign T cells, thus delaying diagnosis and the development of targeted treatments. Here we applied single-cell methods to assess the transcriptional profiles of both malignant T-cell clones and reactive T lymphocytes directly in mycosis fungoides/Sézary syndrome patient samples.

EXPERIMENTAL DESIGN

Single-cell RNA sequencing was used to profile the T-cell immune repertoire simultaneously with gene expression in CD3+ lymphocytes from mycosis fungoides and healthy skin biopsies as well as from Sézary syndrome and control blood samples. Transcriptional data were validated in additional advanced-stage mycosis fungoides/Sézary syndrome skin and blood samples by immunofluorescence microscopy.

RESULTS

Several nonoverlapping clonotypes are expanded in the skin and blood of individual advanced-stage mycosis fungoides/Sézary syndrome patient samples, including a dominant malignant clone as well as additional minor malignant and reactive clones. While we detected upregulation of patient-specific as well as mycosis fungoides- and Sézary syndrome-specific oncogenic pathways within individual malignant clones, we also detected upregulation of several common pathways that included genes associated with cancer cell metabolism, cell-cycle regulation, de novo nucleotide biosynthesis, and invasion.

CONCLUSIONS

Our analysis unveils new insights into mycosis fungoides/Sézary syndrome pathogenesis by providing an unprecedented report of the transcriptional profile of malignant T-cell clones in the skin and blood of individual patients and offers novel prospective targets for personalized therapy.

Clinical, Diagnostic and Prognostic Characteristics of Primary Cutaneous Gamma Delta T-cell Lymphomas

Primary cutaneous γδ T-cell lymphoma (PCGDTL) is a rare subtype of non-Hodgkin lymphoma (NHL) that arises from T-cells with γδ T-cell receptors. The exact incidence of PCGDTL is unknown, as it is usually lumped with other cutaneous lymphomas, which are also uncommon. It is one of the peripheral T-cell lymphoma (PTCL) subtypes which is known to have a dismal prognosis due to poor response and the paucity of available therapies. Despite the rarity and uncertainties of PCGDTL, a number of studies over the past decade were published about the pathologic, diagnostic, cytogenetic and clinical features of this disease. These diagnostic advances will open the doors to explore new therapeutics for this rare entity, specifically targeted and immune therapies. In this review, we highlight these advances, summarize the contemporary treatment approaches, and shed the light on future potential therapeutic targets.

IRF4 drives clonal evolution and lineage choice in a zebrafish model of T-cell lymphoma

IRF4 is a master regulator of immunity and is also frequently overexpressed in mature lymphoid neoplasms. Here, we demonstrate the oncogenicity of IRF4 in vivo, its potential effects on T-cell development and clonal evolution using a zebrafish model. IRF4-transgenic zebrafish develop aggressive tumors with massive infiltration of abnormal lymphocytes that spread to distal organs. Many late-stage tumors are mono- or oligoclonal, and tumor cells can expand in recipient animals after transplantation, demonstrating their malignancy. Mutation of p53 accelerates tumor onset, increases penetrance, and results in tumor heterogeneity. Surprisingly, single-cell RNA-sequencing reveals that the majority of tumor cells are double-negative T-cells, many of which express tcr-γ that became dominant as the tumors progress, whereas double-positive T-cells are largely diminished. Gene expression and epigenetic profiling demonstrates that gata3, mycb, lrrn1, patl1 and psip1 are specifically activated in tumors, while genes responsible for T-cell differentiation including id3 are repressed. IRF4-driven tumors are sensitive to the BRD inhibitor.

Gamma/Delta (γδ) T Cells: The Role of the T-Cell Receptor in Diagnosis and Prognosis of Hematologic Malignancies

ABSTRACT

There are 2 types of T cells: αβ and γδ T cells, named based on the composition of the T-cell receptor. γδ T cells are rare, making up 0.5%-10% of T cells. Although most leukemias, lymphomas, and immune-mediated conditions derive from αβ T cells, a handful of rare but important diseases are generally derived from γδ T cells, particularly primary cutaneous γδ T-cell lymphoma, hepatosplenic T-cell lymphoma, and monomorphic epitheliotropic intestinal T-cell lymphoma. There are also malignancies that may evince a γδ TCR phenotype, including large granulocytic lymphocyte leukemia, T-cell acute lymphobplastic leukemia (T-ALL), and mycosis fungoides, although such cases are rare. In this article, we will review the genesis of the T-cell receptor, the role of γδ T cells, and the importance of TCR type and methods of detection and outline the evidence for prognostic significance (or lack thereof) in lymphomas of γδ T cells. We will also highlight conditions that rarely may present with a γδ TCR phenotype and assess the utility of testing for TCR type in these diseases.

γδ T Cell in Cerebral Ischemic Stroke: Characteristic, Immunity-Inflammatory Role, and Therapy

Gamma-delta (γδ) T cells are a small subset of T cells that are reported to have a proinflammatory role in the pathophysiology of cerebral ischemia stroke (CIS). Upon activation by interleukin-1 beta (IL-1β), IL-23 and IL-18, γδ T cells are stimulated to secrete various cytokines, such as IL-17a, IL-21, IL-22, and interferon-gamma (IFN-γ). In addition, they all play a pivotal role in the inflammatory and immune responses in ischemia. Nevertheless, the exact mechanisms responsible for γδ T cell proinflammatory functions remain poorly understood, and more effective therapies targeting at γδ T cells and cytokines they release remain to be explored, particularly in the context of CIS. CIS is the second most common cause of death and the major cause of permanent disability in adults worldwide. In this review, we focus on the neuroinflammatory and immune functions of γδ T cells and related cytokines, intending to understand their roles in CIS, which may be crucial for the development of novel effective clinical applications.

Critical Role of Flow Cytometric Immunophenotyping in the Diagnosis, Subtyping, and Staging of T-Cell/NK-Cell Non-Hodgkin's Lymphoma in Real-World Practice: A Study of 232 Cases From a Tertiary Cancer Center in India

Background

T-cell/NK-cell non-Hodgkin’s lymphoma (T/NK-NHL) is an uncommon heterogeneous group of diseases. The current classification of T/NK-NHL is mainly based on histopathology and immunohistochemistry. In practice, however, the lack of unique histopathological patterns, overlapping cytomorphology, immunophenotypic complexity, inadequate panels, and diverse clinical presentations pose a great challenge. Flow cytometric immunophenotyping (FCI) is a gold standard for the diagnosis, subtyping, and monitoring of many hematological neoplasms. However, studies emphasizing the role of FCI in the diagnosis and staging of T/NK-NHL in real-world practice are scarce.

Methods

We included T-cell non-Hodgkin’s lymphoma (T-NHL) patients evaluated for the diagnosis and/or staging of T/NK-NHL using FCI between 2014 and 2020. We studied the utility of FCI in the diagnosis and subtyping of T/NK-NHL and correlated the FCI findings with the results of histopathology/immunohistochemistry. For correlation purposes, patients were categorized under definitive diagnosis and subtyping, inadequate subtyping, inadequate diagnosis, and misdiagnosis based on the findings of each technique.

Results

A total of 232 patients were diagnosed with T/NK-NHL. FCI findings provided definitive diagnoses in 198 patients and subtyping in 187/198 (95.45%) patients. The correlation between FCI and histopathological/immunohistochemistry results (n = 150) demonstrated an agreement on the diagnosis and subtyping in 69/150 (46%) patients. Of the remaining cases, the diagnosis and subtyping were inadequate in 64/150 (42.7%), and 14/150 (9.33%) were misdiagnosed on histopathology/immunohistochemistry results. FCI provided definitive diagnosis and subtyping in 51/64 (79.7%) patients. Among these, 13 patients diagnosed with peripheral T-cell lymphoma not-otherwise-specified were reclassified (angioimmunoblastic T-cell lymphoma (AITL)-11 and prolymphocytic leukemia-2) on FCI. It corrected the diagnosis in 14 patients that were misdiagnosed (6 B-cell NHL (B-NHL), 3 Hodgkin’s lymphoma, 1 acute leukemia, and 1 subcutaneous panniculitis-like T-cell lymphoma) and misclassified (3 T-NHL) on histopathological results. AITL was the commonest T-NHL misclassified on histopathological results. FCI also confirmed the definite involvement in 7/83 (8.4%) and 27/83 (32.5%) bone marrow (BM) samples reported as suspicious and uninvolved, respectively, on histopathological evaluation.

Conclusion

AITL was the most frequently diagnosed T/NK-NHL in this study. FCI provided a distinct advantage in detecting BM involvement by T/NK-NHL, especially in patients with low-level involvement. Overall, our study concluded that FCI plays a critical role in the diagnosis, subtyping, and staging of T/NK-NHL in real-world practice.