Pathology of Peripheral T-Cell Lymphomas: Where Do We Stand?

Role of cytokine in malignant T-cell metabolism and subsequent alternation in T-cell tumor microenvironment

T cells are an important component of adaptive immunity and T-cell-derived lymphomas are very complex due to many functional sub-types and functional elasticity of T-cells. As with other tumors, tissues specific factors are crucial in the development of T-cell lymphomas. In addition to neoplastic cells, T- cell lymphomas consist of a tumor micro-environment composed of normal cells and stroma. Numerous studies established the qualitative and quantitative differences between the tumor microenvironment and normal cell surroundings. Interaction between the various component of the tumor microenvironment is crucial since tumor cells can change the microenvironment and vice versa. In normal T-cell development, T-cells must respond to various stimulants deferentially and during these courses of adaptation. T-cells undergo various metabolic alterations. From the stage of quiescence to attention of fully active form T-cells undergoes various stage in terms of metabolic activity. Predominantly quiescent T-cells have ATP-generating metabolism while during the proliferative stage, their metabolism tilted towards the growth-promoting pathways. In addition to this, a functionally different subset of T-cells requires to activate the different metabolic pathways, and consequently, this regulation of the metabolic pathway control activation and function of T-cells. So, it is obvious that dynamic, and well-regulated metabolic pathways are important for the normal functioning of T-cells and their interaction with the microenvironment. There are various cell signaling mechanisms of metabolism are involved in this regulation and more and more studies have suggested the involvement of additional signaling in the development of the overall metabolic phenotype of T cells. These important signaling mediators include cytokines and hormones. The impact and role of these mediators especially the cytokines on the interplay between T-cell metabolism and the interaction of T-cells with their micro-environments in the context of T-cells lymphomas are discussed in this review article.

Nodal peripheral T-cell lymphoma: Chemotherapy-free management, are we there yet?

Peripheral T-cell lymphomas (PTCLs) are a diverse and uncommon type of lymphoid malignancies with a dismal prognosis. Recent advances in genomic studies have shown recurring mutations that are changing our knowledge of the disease's molecular genetics and pathogenesis. As such, new targeted therapies and treatments to improve disease outcomes are currently being explored. In this review, we discussed the current understanding of the nodal PTCL biology with potential therapeutic implications and gave our insights on the promising novel therapies that are currently under study such as immunotherapy, chimeric antigen receptor T-cell therapy, and oncolytic virotherapy.

Peripheral T-Cell Lymphoma, Not Otherwise Specified - a case report and short literature review

Peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) is the most common subgroup of peripheral T-cell lymphomas (PTCL), and constitutes a diagnosis of exclusion. At presentation, most patients exhibit B symptoms and generalized lymphadenopathy, with or without concomitant extra-nodal involvement. We present a case of a man admitted to the hospital with B symptoms, generalized lymphadenopathy and a pruritic exanthema. Laboratory workup reveled persistent eosinophilia and malignant hypercalcemia. The excisional lymph node biopsy diagnosed PTCL-NOS, and the skin biopsy demonstrated a lichenoid dermatitis, compatible with the presumptive clinical diagnosis of a drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome. The patient was treated with topical betamethasone with good overall response, and initiated the first cycle of chemotherapy before discharge. This case report describes a PTCL-NOS with a concomitant non-lymphoproliferative disease, the challenging diagnostic workup of the two diseases and reinforces the most important features of the lymphoproliferative neoplasm.

Baseline total metabolic tumor volume combined with international peripheral T-cell lymphoma project may improve prognostic stratification for patients with peripheral T-cell lymphoma (PTCL)

Purpose

The aim of this study was to explore the prognostic value of total metabolic tumor volume (TMTV) at baseline ¹⁸F-FDG PET/CT in patients diagnosed with peripheral T-cell lymphoma (PTCL).

Materials and methods

Eighty-four newly diagnosed PTCL patients who underwent baseline ¹⁸F-FDG PET/CT prior to treatment between March 2009 and January 2019 were enrolled in this retrospective study. The FDG-avid lesions in each patient were segmented using semiautomated software to calculate the maximum standardized uptake value (SUVmax), total metabolic tumor volume (TMTV), and total lesion glycolysis (TLG) values using the boundaries of voxels presenting with the 41% SUVmax threshold method. Progression-free survival (PFS) and overall survival (OS) were used as end points to evaluate patient prognosis. The log-rank test and Cox regression analyses were used to evaluate PFS and OS.

Results

ROC curve analysis indicated an ideal TMTV cut-off value of 228.8 cm³. During the 4–131 months (29.2 ± 28.5 months) follow-up period, high TMTV was significantly associated with worse PFS and OS. TMTV and the international peripheral T-cell lymphoma project score (IPTCLP) were independent predictors of PFS and OS with multivariate analysis. The combination of TMTV and the IPTCLP may provide significantly better risk substratification in PFS and OS of PTCL patients.

Conclusions

Both TMTV and IPTCLP are independent predictors of PTCL patient survival outcomes. Moreover, the combination of TMTV and IPTCLP improved patient risk stratification and may contribute to personalized therapeutic regimens.

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

Primary cutaneous γδ T cell lymphomas (PCGDTLs) represent a heterogeneous group of uncommon but aggressive cancers. Herein, we perform genome-wide DNA, RNA, and T cell receptor (TCR) sequencing on 29 cutaneous γδ lymphomas. We find that PCGDTLs are not uniformly derived from Vδ2 cells. Instead, the cell-of-origin depends on the tissue compartment from which the lymphomas are derived. Lymphomas arising from the outer layer of skin are derived from Vδ1 cells, the predominant γδ cell in the epidermis and dermis. In contrast, panniculitic lymphomas arise from Vδ2 cells, the predominant γδ T cell in the fat. We also show that TCR chain usage is non-random, suggesting common antigens for Vδ1 and Vδ2 lymphomas respectively. In addition, Vδ1 and Vδ2 PCGDTLs harbor similar genomic landscapes with potentially targetable oncogenic mutations in the JAK/STAT, MAPK, MYC, and chromatin modification pathways. Collectively, these findings suggest a paradigm for classifying, staging, and treating these diseases.

Approach to nodal-based T-cell lymphomas

Peripheral T-cell lymphomas (PTCLs) represent a heterogeneous group of uncommon malignancies derived from mature T cells and usually characterised by an aggressive clinical course. Their clinical presentation, localisation and pattern of dissemination are highly variable, but the majority of cases present as nodal diseases. The recently revised classification of lymphomas has incorporated many new molecular genetic data derived from gene expression profiling and next generation sequencing studies, which refine the definition and diagnostic criteria of several entities. Nevertheless, the distinction of PTCL from various reactive conditions, and the diagnosis of PTCL subtypes remains notably challenging. Here, an updated summary of the clinicopathological and molecular features of the most common nodal-based PTCLs (angioimmunoblastic T-cell lymphoma and other nodal lymphomas derived from follicular T helper cells, anaplastic large cell lymphomas and peripheral T-cell lymphoma, not otherwise specified) is presented. Practical recommendations in the diagnostic approach to nodal T-cell lymphoproliferations are presented, including indications for the appropriate use and interpretation of ancillary studies. Finally, we discuss commonly encountered diagnostic problems, including pitfalls and mimics in the differential diagnosis with various reactive conditions, and the criteria that allow proper identification of distinct PTCL entities.

Prognostic and therapeutic significance of phosphorylated STAT3 and protein tyrosine phosphatase-6 in peripheral-T cell lymphoma

Peripheral T cell lymphomas (PTCL) is a heterogenous group of non-Hodgkin lymphoma and many patients remain refractory to the frontline therapy. Identifying new prognostic markers and treatment is an unmet need in PTCL. We analyzed phospho-STAT3 (pSTAT3) expression in a cohort of 169 PTCL tumors and show overall 38% positivity with varied distribution among PTCL subtypes with 27% (16/59) in PTCL-NOS; 29% (11/38) in AITL, 57% (13/28) in ALK-negative ALCL, and 93% in ALK-pos ALCL (14/15), respectively. Correlative analysis indicated an adverse correlation between pSTAT3 and overall survival (OS). PTPN6, a tyrosine phosphatase and potential negative regulator of STAT3 activity, was suppressed in 62% of PTCL-NOS, 42% of AITL, 60% ALK-neg ALCL, and 86% of ALK-pos ALCL. Loss of PTPN6 combined with pSTAT3 positivity predicted an infwere considered significantferior OS in PTCL cases. In vitro treatment of TCL lines with azacytidine (aza), a DNA methyltransferase inhibitor (DNMTi), restored PTPN6 expression and decreased pSTAT3. Combining DNMTi with JAK3 inhibitor resulted in synergistic antitumor activity in SUDHL1 cell line. Overall, our results suggest that PTPN6 and activated STAT3 can be developed as prognostic markers, and the combination of DNMTi and JAK3 inhibitors as a novel treatment for patients with PTCL subtypes.

Transformation of T-Cell Acute Lymphoblastic Lymphoma to Peripheral T-Cell Lymphoma: A Report of Two Cases

Nonhepatosplenic/noncutaneous γδ peripheral T-cell lymphoma (NHNCγδ PTCL) represents a miscellaneous group of unrelated T-cell lymphomas of which only isolated cases have been reported. We describe two cases of transformation from T-lymphoblastic leukemia/lymphoma to NHNCγδ PTCL. Transformation into more aggressive disease is a rare event in T-cell lineage-derived hematologic malignancies compared to B-cell neoplasms. Nevertheless, both of our cases involved relapse as PTCL manifested with skin involvement and an overt shift from blastic morphology to large granular leukemia-like mature T cells. Among other notable molecular characteristics, expression of immature markers such as TdT was lost in both cases. Based on cytogenetics, phenotype, and morphology, both patients represent a novel phenomenon of clonal transformation from T-ALL to PTCL which has rarely been reported in the literature. Such transformation may carry important diagnostic and biological implications.

Quantitative Analysis of a Multiplexed Immunofluorescence Panel in T-Cell Lymphoma

Immunohistochemistry (IHC) provides clinically useful information on protein expression in cancer cells. However, quantification of colocalizing signals using conventional IHC and visual scores is challenging. Here we describe the application of quantitative immunofluorescence in angioimmunoblastic T-cell lymphoma (AITL), a peripheral T-cell lymphoma characterized by cellular heterogeneity that impedes IHC interpretation and quantification. A multiplexed immunofluorescence (IF) panel comprising T- and B-lymphocyte markers along with T-follicular helper (T_FH) markers was validated for appropriate cellular localization in sections of benign tonsillar tissue and tested in two samples of AITL, using a Vectra microscope for spectral imaging and InForm software for analysis. We measured the percentage positivity of the T_FH markers, BCL6 and PD1, in AITL CD4-positive cells to be approximately 26% and 45%, with 12% coexpressing both markers. The pattern is similar to CD4 cells within the germinal center of normal tonsils and clearly distinct from extragerminal CD4 cells. This study demonstrates the feasibility of automated and quantitative imaging of a multiplexed panel of cellular markers in formalin-fixed, paraffin-embedded tissue sections of a cellularly heterogenous lymphoma. Multiplexed IF allows the simultaneous scoring of markers in malignant and immune cell populations and could potentially increase accuracy for establishment of diagnostic thresholds.

Emerging therapeutic targets in myeloproliferative neoplasms and peripheral T-cell leukemia and lymphomas

Introduction: Hematopoietic neoplasms are often driven by gain-of-function mutations of the JAK-STAT pathway together with mutations in chromatin remodeling and DNA damage control pathways. The interconnection between the JAK-STAT pathway, epigenetic regulation or DNA damage control is still poorly understood in cancer cell biology.

Areas covered: Here, we focus on a broader description of mutational insights into myeloproliferative neoplasms and peripheral T-cell leukemia and lymphomas, since sequencing efforts have identified similar combinations of driver mutations in these diseases covering different lineages. We summarize how these pathways might be interconnected in normal or cancer cells, which have lost differentiation capacity and drive oncogene transcription.

Expert opinion: Due to similarities in driver mutations including epigenetic enzymes, JAK-STAT pathway activation and mutated checkpoint control through TP53, we hypothesize that similar therapeutic approaches could be of benefit in these diseases. We give an overview of how driver mutations in these malignancies contribute to hematopoietic cancer initiation or progression, and how these pathways can be targeted with currently available tools.

Autologous and Allogeneic Hematopoietic Cell Transplantation in Peripheral T/NK-cell Lymphomas: A Histology-Specific Review

Peripheral T-cell lymphoma and natural killer/T-cell lymphomas (PT/NKCL) make up a diverse subgroup of non-Hodgkin's lymphomas characterized by an aggressive clinical course. The use of hematopoietic stem cell transplantation (HSCT) in the treatment of PT/NKCL remains controversial because of the absence of randomized controlled trials. The best available data suggest that certain subtypes of PT/NKCL may benefit more from the application of HSCT than other subtypes and that this benefit results from their unique clinical characteristics and underlying biology. Ultimately, however, prospective randomized controlled trials are needed to clarify the optimal type and timing of HSCT in patients with PT/NKCL.

Assessment of tumor-infiltrating TCRV9V2 lymphocyte abundance by deconvolution of human cancers microarrays

Most human blood γδ cells are cytolytic TCRVγ9Vδ2⁺ lymphocytes with antitumor activity. They are currently investigated in several clinical trials of cancer immunotherapy but so far, their tumor infiltration has not been systematically explored across human cancers. Novel algorithms allowing the deconvolution of bulk tumor transcriptomes to find the relative proportions of infiltrating leucocytes, such as CIBERSORT, should be appropriate for this aim but in practice they fail to accurately recognize γδ T lymphocytes. Here, by implementing machine learning from microarray data, we first improved the computational identification of blood-derived TCRVγ9Vδ2⁺ γδ lymphocytes and then applied this strategy to assess their abundance as tumor infiltrating lymphocytes (γδ TIL) in ∼10,000 cancer biopsies from 50 types of hematological and solid malignancies. We observed considerable inter-individual variation of TCRVγ9Vδ2⁺γδ TIL abundance both within each type and across the spectrum of cancers tested. We report their prominence in B cell-acute lymphoblastic leukemia (B-ALL), acute promyelocytic leukemia (M3-AML) and chronic myeloid leukemia (CML) as well as in inflammatory breast, prostate, esophagus, pancreas and lung carcinoma. Across all cancers, the abundance of αβ TILs and TCRVγ9Vδ2⁺ γδ TILs did not correlate. αβ TIL abundance paralleled the mutational load of tumors and positively correlated with inflammation, infiltration of monocytes, macrophages and dendritic cells (DC), antigen processing and presentation, and cytolytic activity, in line with an association with a favorable outcome. In contrast, the abundance of TCRVγ9Vδ2⁺ γδ TILs did not correlate with these hallmarks and was variably associated with outcome, suggesting that distinct contexts underlie TCRVγ9Vδ2⁺ γδ TIL and αβ TIL mobilizations in cancer.

Cutaneous CD8+ Cytotoxic T-Cell Lymphoma Infiltrates: Clinicopathological Correlation and Outcome of 35 Cases

Introduction

Cytotoxic CD8+ T-cell lymphomas are only rarely encountered and thus remain only poorly characterized. Our aim was to collect and correlate clinical and histological data of CD8+ skin lymphoma infiltrates to obtain a proper subtype assignment of CD8+ skin lymphoma infiltrates and to derive putative prognostic markers thereof.

Methods

Formalin-fixed and paraffin-embedded (FFPE) tissue of 35 patients with CD8+ cytotoxic cutaneous T-cell lymphoma infiltrates was retrieved from the archives of the Institute of Pathology and the Department of Dermatology, University Hospital Wuerzburg, dating back from 1998 until 2015. Cytological, histological, immunohistochemical and molecular genetic features were assessed and correlated with respective clinical data.

Results

The identified cases of CD8+ cytotoxic atypical lymphoproliferative infiltrates of the skin (n = 35) comprised 13 cases of mycosis fungoides (MF)/Sézary syndrome (SS), 4 cases of subcutaneous panniculitis-like T-cell lymphoma (SPTCL), 5 cases of primary cutaneous acral CD8+ lymphoma [formerly indolent CD8+ lymphoid proliferation (ILP)] and 1 case of aggressive epidermotropic primary cutaneous T-cell lymphoma (AECTCL). Moreover, nine cases were classified as primary cutaneous peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) and three cases as systemic PTCL-NOS. Multiple skin lesions, a high proliferative index and especially a final subtype attribution to AECTCL or systemic PTCL-NOS were associated with a worse survival. Coexpression of CD68 by tumor cells was exclusively observed in indolent acral CD8+ T-cell lymphoma and thus indicated an invariably benign clinical course. No further distinctive markers could be derived from our analysis.

Conclusion

Cutaneous infiltrates of CD8+ cytotoxic T-cell lymphoma comprise clinically and histologically heterogeneous entities of either primary cutaneous T-cell lymphomas or secondary infiltrates of otherwise systemic peripheral T-cell lymphomas. A thorough clinicopathological correlation with respective staging examinations remains the mainstay for correct subtype assignment and proper prognostication as long as no better markers have been defined.

Activating mutations in genes related to TCR signaling in angioimmunoblastic and other follicular helper T-cell-derived lymphomas

Angioimmunoblastic T-cell lymphoma (AITL) and other lymphomas derived from follicular T-helper cells (TFH) represent a large proportion of peripheral T-cell lymphomas (PTCLs) with poorly understood pathogenesis and unfavorable treatment results. We investigated a series of 85 patients with AITL (n = 72) or other TFH-derived PTCL (n = 13) by targeted deep sequencing of a gene panel enriched in T-cell receptor (TCR) signaling elements. RHOA mutations were identified in 51 of 85 cases (60%) consisting of the highly recurrent dominant negative G17V variant in most cases and a novel K18N in 3 cases, the latter showing activating properties in in vitro assays. Moreover, half of the patients carried virtually mutually exclusive mutations in other TCR-related genes, most frequently in PLCG1 (14.1%), CD28 (9.4%, exclusively in AITL), PI3K elements (7%), CTNNB1 (6%), and GTF2I (6%). Using in vitro assays in transfected cells, we demonstrated that 9 of 10 PLCG1 and 3 of 3 CARD11 variants induced MALT1 protease activity and increased transcription from NFAT or NF-κB response element reporters, respectively. Collectively, the vast majority of variants in TCR-related genes could be classified as gain-of-function. Accordingly, the samples with mutations in TCR-related genes other than RHOA had transcriptomic profiles enriched in signatures reflecting higher T-cell activation. Although no correlation with presenting clinical features nor significant impact on survival was observed, the presence of TCR-related mutations correlated with early disease progression. Thus, targeting of TCR-related events may hold promise for the treatment of TFH-derived lymphomas.

CD1d-restricted peripheral T cell lymphoma in mice and humans

Peripheral T cell lymphomas (PTCLs) are a heterogeneous entity of neoplasms with poor prognosis, lack of effective therapies, and a largely unknown pathophysiology. Identifying the mechanism of lymphomagenesis and cell-of-origin from which PTCLs arise is crucial for the development of efficient treatment strategies. In addition to the well-described thymic lymphomas, we found that p53-deficient mice also developed mature PTCLs that did not originate from conventional T cells but from CD1d-restricted NKT cells. PTCLs showed phenotypic features of activated NKT cells, such as PD-1 up-regulation and loss of NK1.1 expression. Injections of heat-killed Streptococcus pneumonia, known to express glycolipid antigens activating NKT cells, increased the incidence of these PTCLs, whereas Escherichia coli injection did not. Gene expression profile analyses indicated a significant down-regulation of genes in the TCR signaling pathway in PTCL, a common feature of chronically activated T cells. Targeting TCR signaling pathway in lymphoma cells, either with cyclosporine A or anti-CD1d blocking antibody, prolonged mice survival. Importantly, we identified human CD1d-restricted lymphoma cells within Vδ1 TCR-expressing PTCL. These results define a new subtype of PTCL and pave the way for the development of blocking anti-CD1d antibody for therapeutic purposes in humans.

Mature T- and NK-cell non-Hodgkin lymphoma in children and young adolescents

Mature T/Natural killer (NK)-cell neoplasms of children and the young adolescent population exhibit higher prevalence in Central and South American and Asian populations and many are associated with Epstein-Barr virus (EBV). They are represented in large part by extranodal T/NK cell lymphomas- nasal-type or extra nasal-type, chronic lymphoproliferative disorders of T/NK cells or chronic active EBV disease, systemic EBV-positive lymphoproliferative disorders of childhood, hydroa vacciniforme-like lymphoma, hepatosplenic T-cell lymphoma and primary cutaneous gamma/delta T-cell lymphoma among others. Many T/NK cell neoplasms in this age group are derived from cells of the innate immune system, in contrast to adults where they are predominantly from the adaptive immune system. The genetic basis of T/NK cell lymphomas in children and young adolescents remains largely unknown. Anthracycline-based regimens and haematopoietic stem cell transplants (allogeneic and autologous) are current treatment modalities, however it is anticipated that novel targeted therapeutic agents will be available in the near future.

The European Hematology Association Roadmap for European Hematology Research: a consensus document

The European Hematology Association (EHA) Roadmap for European Hematology Research highlights major achievements in diagnosis and treatment of blood disorders and identifies the greatest unmet clinical and scientific needs in those areas to enable better funded, more focused European hematology research. Initiated by the EHA, around 300 experts contributed to the consensus document, which will help European policy makers, research funders, research organizations, researchers, and patient groups make better informed decisions on hematology research. It also aims to raise public awareness of the burden of blood disorders on European society, which purely in economic terms is estimated at €23 billion per year, a level of cost that is not matched in current European hematology research funding. In recent decades, hematology research has improved our fundamental understanding of the biology of blood disorders, and has improved diagnostics and treatments, sometimes in revolutionary ways. This progress highlights the potential of focused basic research programs such as this EHA Roadmap.The EHA Roadmap identifies nine 'sections' in hematology: normal hematopoiesis, malignant lymphoid and myeloid diseases, anemias and related diseases, platelet disorders, blood coagulation and hemostatic disorders, transfusion medicine, infections in hematology, and hematopoietic stem cell transplantation. These sections span 60 smaller groups of diseases or disorders.The EHA Roadmap identifies priorities and needs across the field of hematology, including those to develop targeted therapies based on genomic profiling and chemical biology, to eradicate minimal residual malignant disease, and to develop cellular immunotherapies, combination treatments, gene therapies, hematopoietic stem cell treatments, and treatments that are better tolerated by elderly patients.

Comprehensive serum cytokine analysis identifies IL-1RA and soluble IL-2Rα as predictors of event-free survival in T-cell lymphoma

BACKGROUND

T-cell malignancies are heterogeneous in their clinical presentation and pathology, and have a poor prognosis. New biomarkers are needed to predict prognosis and to provide insights into signal pathways used by these cells. The goal of this study was to evaluate pretreatment serum cytokines in patients with newly diagnosed T-cell neoplasms and correlate with clinical outcome.

PATIENTS AND METHODS

We evaluated 30 cytokines in pretreatment serum from 68 untreated patients and 14 normal controls. Significantly elevated cytokines were correlated with patterns of abnormalities, event-free survival (EFS) and overall survival (OS).

RESULTS

Our data demonstrated significantly elevated levels (versus controls) of seven cytokines-epidermal growth factor (EGF), IL-6, IL-12, interferon gamma-induced protein (IP)-10, soluble interleukin (sIL)-2Rα, monokine induced by gamma interferon (MIG), and IL-1RA-in all T-cell neoplasms (P < 0.05). In the angioimmunoblastic subset, all seven cytokines except IP-10 and in the peripheral T-cell lymphoma (TCL)-not otherwise specified subset, only IP-10, sIL-2Rα, MIG, and IL-8 were statistically elevated compared with control. Of these, elevated cytokines all but EGF were predictive of an inferior EFS; IL-1RA, sIL-2Rα, and MIG predicted an inferior OS. In a multivariate analysis, sIL-2Rα [hazard ratio (HR) = 3.95; 95% confidence interval (CI) 1.61-8.38] and IL-1RA (HR = 3.28; 95% CI 1.47-7.29) levels remained independent predictors of inferior EFS. TCL cell lines secreted high levels of sIL-2Rα and expressed the IL-2Rα surface receptor.

CONCLUSIONS

This report describes the cytokines relevant to prognosis in patients with untreated TCL and provides the rationale to include serum IL-1RA and sIL-2Rα as biomarkers in future trials. Inhibition of these cytokines may also be of therapeutic benefit.

Pathology of T-cell lymphomas: diagnosis and biomarker discovery

T-cell lymphomas are a group of predominantly rare hematologic malignancies that tend to recapitulate different stages of T-cell development, in a similar way that B-cell lymphomas do. As opposed to B-cell lymphomas, the understanding of the biology and the classification of T-cell lymphomas are somewhat rudimentary, and numerous entities are still included as 'provisional categories' in the World Health Classification of hematolopoietic malignancies. A relevant and useful classification of these disorders have been difficult to accomplish because of the rarity nature of them, the relative lack of understanding of the molecular pathogenesis, and their morphological and immunophenotypical complexity. Overall, T-cell lymphomas represent only 15 % of all non-Hodgkin lymphomas. This review is focused on addressing the current status of the categories of mature T-cell leukemias and lymphomas (nodal and extranodal) using an approach that incorporates histopathology, immunophenotype, and molecular understanding of the nature of these disorders, using the same philosophy of the most recent revised WHO classification of hematopoietic malignancies.