Peripheral T cell lymphomas with follicular T helper phenotype: a new basket or a distinct entity? Revising Karl Lennert’s personal archive

Pathobiology of nodal peripheral T-cell lymphomas: current understanding and future directions

Predominantly nodal is the most common clinical presentation of peripheral T- (and NK-) cell lymphomas (PTCL), which comprise three main groups of diseases: (i) systemic anaplastic large cell lymphomas (ALCL), whether positive or negative for anaplastic lymphoma kinase (ALK); (ii) follicular helper T-cell lymphomas (TFHL); and (iii) PTCL, not otherwise specified (NOS). Recent advances in the genomic and molecular characterization of PTCL, with enhanced understanding of pathobiology, have translated into significant updates in the latest 2022 classifications of lymphomas. ALK-negative ALCL is now recognized to be genetically heterogeneous, with identification of DUSP22 rearrangements in approximately 20-30% of cases, correlated with distinctive pathological and biological features. The notion of cell-of-origin as an important determinant of the classification of nodal PTCL is best exemplified by TFHL, considered as one disease or a group of related entities, sharing oncogenic pathways with frequent recurrent epigenetic mutations as well as a relationship to clonal hematopoiesis. Data are emerging to support that a similar cell-of-origin concept might be relevant to characterize meaningful subgroups within PTCL, NOS, based on cytotoxic and/or Th1 versus Th2 signatures. The small group of primary nodal Epstein-Barr virus-positive lymphomas of T- or NK-cell derivation, formerly considered PTCL, NOS, is now classified separately, due to distinctive features, and notably an aggressive course. This review summarizes current knowledge of the pathology and biology of nodal-based PTCL entities, with an emphasis on recent findings and underlying oncogenic mechanisms.

Peripheral T-cell lymphoma with a T follicular-helper phenotype: A different entity? Results of the Spanish Real-T study

Nodal peripheral T-cell lymphoma (PTCL) with a T follicular helper phenotype (PTCL-TFH) is a new type of PTCL. We aimed to define its clinical characteristics and prognosis compared to PTCL not otherwise specified (PTCL-NOS) and angioimmunoblastic T-cell lymphoma (AITL). This retrospective observational study included 175 patients diagnosed with PTCL between 2008 and 2013 in 13 Spanish sites. Patient diagnosis was centrally reviewed, and patients were reclassified according to the World Health Organization (WHO) 2016 criteria: 21 patients as PTCL-NOS, 55 as AITL and 23 as PTCL-TFH. Median follow-up was 56.07 months (95% CI 38.7-73.4). Progression-free survival (PFS) and overall survival (OS) were significantly higher in patients with PTCL-TFH than in those with PTCL-NOS and AITL (PFS, 24.6 months vs. 4.6 and 7.8 months, respectively, p = 0.002; OS, 52.6 months vs. 10.0 and 19.3 months, respectively, p < 0.001). Histological diagnosis maintained an independent influence on both PFS (hazard ratio [HR] 4.1 vs. PTCL-NOS, p = 0.008; HR 2.6 vs. AITL, p = 0.047) and OS (HR 5.7 vs. PTCL-NOS, p = 0.004; HR 2.6 vs. AITL, p = 0.096), regardless of the International Prognostic Index. These results suggest that PTCL-TFH could have more favourable features and prognosis than the other PTCL subtypes, although larger series are needed to corroborate these findings.

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.

Follicular helper T-cell lymphomas: disease spectrum, relationship with clonal hematopoiesis, and mimics. A report of the 2022 EA4HP/SH lymphoma workshop

Follicular helper T-cell lymphomas (TFH lymphomas) were discussed in session V of the lymphoma workshop of the European Association for Haematopathology (EA4HP)/Society for Hematopathology (SH) 2022 meeting in Florence, Italy. The session focused on the morphologic spectrum of TFH lymphoma, including its three subtypes: angioimmunoblastic-type (AITL), follicular-type, and not otherwise specified (NOS). The submitted cases encompassed classic examples of TFH lymphoma and unusual cases such as those with early or indolent presentations, associated B-cell proliferations, or Hodgkin/Reed-Sternberg-like cells. The relationship between TFH lymphoma and clonal hematopoiesis was highlighted by several cases documenting divergent evolution of myeloid neoplasm and AITL from shared clonal mutations. The distinction between TFH lymphoma and peripheral T-cell lymphoma, not otherwise specified (PTCL, NOS), was stressed, and many challenging examples were presented. Various cases highlighted the difficulties of differentiating TFH lymphoma from other established types of lymphoma and reactive conditions. Cutaneous T-cell lymphoma expressing TFH markers, particularly when resulting in lymph node involvement, should be distinguished from TFH lymphomas. Additional immunophenotyping and next-generation sequencing studies were performed on various cases in this session, highlighting the importance of these technologies to our current understanding and classification of TFH lymphomas.

Pathologic and molecular insights in nodal T-follicular helper cell lymphomas

T-follicular helper (TFH) cells are one of the T-cell subsets with a critical role in the regulation of germinal center (GC) reactions. TFH cells contribute to the positive selection of GC B-cells and promote plasma cell differentiation and antibody production. TFH cells express a unique phenotype characterized by PD-1^hi, ICOS^hi, CD40L^hi, CD95^hi, CTLA^hi, CCR7^lo, and CXCR5^hi . Three main subtypes of nodal TFH lymphomas have been described: 1) angioimmunoblastic-type, 2) follicular-type, and 3) not otherwise specified (NOS). The diagnosis of these neoplasms can be challenging, and it is rendered based on a combination of clinical, laboratory, histopathologic, immunophenotypic, and molecular findings. The markers most frequently used to identify a TFH immunophenotype in paraffin-embedded tissue sections include PD-1, CXCL13, CXCR5, ICOS, BCL6, and CD10. These neoplasms feature a characteristic and similar, but not identical, mutational landscape with mutations in epigenetic modifiers (TET2, DNMT3A, IDH2), RHOA, and T-cell receptor signaling genes. Here, we briefly review the biology of TFH cells and present a summary of the current pathologic, molecular, and genetic features of nodal lymphomas. We want to highlight the importance of performing a consistent panel of TFH immunostains and mutational studies in TCLs to identify TFH lymphomas.

Precise diagnosis and targeted therapy of nodal T-follicular helper cell lymphoma (T-FHCL)

Nodal T-follicular helper cell lymphoma (T-FHCL) derived from T-follicular helper (Tfh) cell falls into a heterogeneous category of peripheral T-cell lymphoma (PTCL). Due to the limited number of therapeutic regimens and limited first-line efficacy, T-FHCL has a poor prognosis, and there is an urgent need for effective targeted therapies. With advancements in sequencing technologies, especially single-cell sequencing and next-generation sequencing, more specific genetic aberrations characteristic of T-FHCL can be discovered, allowing for precise molecular diagnosis and specific research on novel agents. Many biomarker-targeting agents, used either alone or in combination, have been tested, and they have generally enhanced the therapeutic outcomes of T-FHCL. Histone deacetylase inhibitors achieve significant clinical benefits in the treatment of T-FHCL, especially in combination therapy. Chimeric antigen receptor T-cell (CAR-T-cell) immunotherapies, hematopoietic stem cell transplantation, and other potential agents merit further study.

An Isolated Mesenteric Presentation of a Nodal Peripheral T Cell Lymphoma with T Follicular Helper Cell Phenotype

Nodal peripheral T cell lymphoma (PTCL) with T follicular helper (TFH) cell phenotype is a provisional entity added to the 2016 revised WHO classification of haematological malignancies. These lymphomas have an aggressive clinical course and respond poorly to conventional treatments. Distinct histological features have not been well described. Additionally, the minimum criteria for diagnosis is not well established but detection of at least two TFH markers in addition to CD4 is suggested to assign a TFH cell phenotype. Some pathological features of angioimmunoblastic T cell lymphoma (AITL) such as recurrent molecular alterations are commonly found. As the name suggests, these lymphomas are nodal in origin with patients presenting with widespread lymphadenopathy. We describe the first documented case of nodal PTCL with a TFH phenotype presenting as an isolated mesenteric mass with no nodal involvement.

Incidence and clinicopathological features of Follicular T-cell lymphoma in Finland; a population-based immunohistochemical study

Follicular T-cell lymphoma (FTCL) is a rare subtype of mature T-cell lymphoma. It was recently recognized as a separate lymphoma entity in the 2017 revised 4th edition of the WHO classification. The main goals of the present study were to gain better knowledge of the incidence and histopathological and clinical features of FTCL in Finland. In this study, we reviewed all angioimmunoblastic T-cell (AITL) and peripheral T-cell lymphomas, not otherwise specified, from the patient records in three hospital districts in Finland over a 10-year period, to identify FTCL cases and estimate its incidence. Five patients rediagnosed with FTCL and thirty-four with AITL were analyzed. Hodgkin/Reed-Sternberg (HRS)-like cells were observed in 24 of the 34 AITL cases and 4 of the 5 FTCL cases. We found that the main features that differentiated FTCL from AITL were the presence of clear cells, rosetting of T-cells around HRS-like cells, follicular dendritic cell meshwork, and T-cell monoclonality. Our estimated incidence of FTCL is 0.20 per 100,000 people in Finland.

Virus-Driven Carcinogenesis

Cancer arises from the accumulation of genetic and epigenetic alterations. Even in the era of precision oncology, carcinogens contributing to neoplastic process are still an important focus of research. Comprehensive genomic analyses have revealed various combinations of base substitutions, referred to as the mutational signatures, in cancer. Each mutational signature is believed to arise from specific DNA damage and repair processes, including carcinogens. However, as a type of carcinogen, tumor viruses increase the cancer risk by alternative mechanisms, including insertional mutagenesis, viral oncogenes, and immunosuppression. In this review, we summarize virus-driven carcinogenesis to provide a framework for the control of malignant cell proliferation. We first provide a brief overview of oncogenic viruses and describe their implication in virus-related tumors. Next, we describe tumor viruses (HPV, Human papilloma virus; HBV, Hepatitis B virus; HCV, Hepatitis C virus; EBV, Epstein-Barr virus; Kaposi sarcoma herpesvirus; MCV, Merkel cell polyoma virus; HTLV-1, Human T-cell lymphotropic virus, type-1) and tumor virus-related cancers. Lastly, we introduce emerging tumor virus candidates, human cytomegalovirus (CMV), human herpesvirus-6 (HHV-6) and adeno-associated virus-2 (AAV-2). We expect this review to be a hub in a complex network of data for virus-associated carcinogenesis.

American Registry of Pathology Expert Opinions: Recommendations for the diagnostic workup of mature T cell neoplasms

The diagnosis of T-cell lymphomas is highly challenging and requires an integrated approach in which clinical, morphologic, immunophenotypic and molecular data are incorporated into the diagnosis. Under the auspices of the American Registry of Pathology, the authors met to discuss this topic with the goal to provide practical and useful recommendations for pathologists when evaluating T-cell lymphomas. In this review, we discuss the diagnostic findings and workup for the various types of nodal T-cell lymphoma including anaplastic large cell lymphoma, nodal peripheral T-cell lymphoma not otherwise specified (PTCL-NOS), and PTCL with a T follicular helper (TFH) phenotype. We review clinicopathologic and immunophenotypic features (including flow cytometry panels) helpful in the differential diagnosis of mature T-cell lymphomas presenting in the peripheral blood and bone marrow, and we discuss some of the more common extranodal-based T-cell lymphomas including extranodal natural killer/T-cell lymphoma of nasal and non-nasal type, gamma delta T cell lymphomas, and aggressive and indolent T- and NK-lymphoproliferative disorders involving the gastrointestinal tract. Mycosis fungoides and most other cutaneous T-cell lymphomas are not the focus of this review, although the differential diagnosis of Sezary syndrome from mycosis fungoides is covered. We do not intend for these recommendations to be anything other than suggestions that will hopefully spur on additional discussion, and perhaps eventually evolve into a consensus approach for the workup of T-cell lymphomas.

RHOA mutation in follicular T-cell lymphoma: Clinicopathological analysis of 16 cases

Follicular T-cell lymphoma (FTCL) is considered to originate from follicular helper T-cell (Tfh) cells. Angioimmunoblastic T-cell lymphoma (AITL) and peripheral T-cell lymphomas with the Tfh phenotype, derived from Tfh cells, often harbor RHOA G17V mutation. We investigated whether RHOA mutations affect the clinicopathological features of FTCL. We performed deep sequencing and Sanger sequencing for RHOA exon 2 in 16 cases of FTCL. Nine cases showed RHOA mutations, including eight with c.G50T, p.Gly17Val and one with c.G50A, p.Gly17Glu, c.A52G, p.Lys18Glu, c.T102C, p.Tyr34Tyr and c.G145T, p.Asp49Tyr. Compared to the RHOA mutation-negative group, the RHOA mutation-positive group had a higher tendency for B-immunoblasts (P = 0.06), the AITL component (P = 0.09), and higher positive rate for CD10 (P = 0.09) and BCL6 (P = 0.09), and a significantly higher positive rate for CXCL13 (P = 0.04). Although not statistically significant, the RHOA mutation-positive group showed higher values for almost all characteristic AITL features. There was no significant difference in overall survival between RHOA mutation-positive and -negative groups. The RHOA mutation may play an important role in clinicopathological characteristics and lymphomagenesis of FTCL. A more detailed investigation is needed to highlight the importance of RHOA mutations in FTCL.

Genomics of Peripheral T-Cell Lymphoma and Its Implications for Personalized Medicine

Peripheral T-cell lymphoma (PTCL) is a rare, heterogenous group of mature T-cell neoplasms that comprise 10–15% of non-Hodgkin lymphoma cases in the United States. All subtypes of PTCL, except for ALK⁺ anaplastic T-cell lymphoma, are associated with poor prognosis, with median overall survival (OS) rates of 1–3 years. The diagnosis of PTCL is mainly based on clinical presentation, morphologic features, and immunophenotypes. Recent advances in genome sequencing and gene expression profiling have given new insights into the pathogenesis and molecular biology of PTCL. An enhanced understanding of its genomic landscape holds the promise of refining the diagnosis, prognosis, and management of PTCL. In this review, we examine recently discovered genetic abnormalities identified by molecular profiling in 3 of the most common types of PTCL: RHOA^G17V and epigenetic regulator mutations in angioimmunoblastic T-cell lymphoma, ALK expression and JAK/STAT3 pathway mutations in anaplastic T-cell lymphoma, and T-follicular helper phenotype and GATA3/TBX21 expression in PTCL-not otherwise specified. We also discuss the implications of these abnormalities for clinical practice, new/potential targeted therapies, and the role of personalized medicine in the management of PTCL.

Application of a 5 Marker Panel to the Routine Diagnosis of Peripheral T-Cell Lymphoma With T-Follicular Helper Phenotype

The 2017 World Health Organization update introduced a new category of nodal peripheral T-cell lymphoma with T-follicular helper phenotype (PTCL-TFH) defined by expression of at least 2 or 3 TFH markers. Our study assesses the utility of an immunohistochemical panel of 5 TFH markers (CD10, BCL6, PD-1, CXCL13, and ICOS) for identification of TFH phenotype in angioimmunoblastic T-cell lymphoma (AITL) and PTCL not otherwise specified (NOS). Immunohistochemical for the 5 markers was performed on 22 cases of AITL and 29 cases of PTCL-NOS. Cases were reviewed for morphologic features characteristic of AITL. All AITL cases showed expression of ≥2 TFH markers. This panel resulted in reclassification of 41% PTCL-NOS cases to PTCL-TFH. Positive percent agreement for the TFH phenotype is 97% for PD1, 94% for ICOS, 44% for CD10 and CXCL13, and 29% for BCL6. Negative percent agreement for TFH phenotype is 100% for CD10, BCL6, and CXCL13, 82% for ICOS and 71% for PD1. AITL cases were more likely than PTCL-TFH cases to contain expanded CD21-positive follicular dendritic cell meshworks, clear cell cytology and polymorphous inflammatory background; however, there was a significant (P<0.005) Kruskal-Wallis trend in all morphologic variables between the 3 groups suggesting a continuum from PTCL-NOS to PTCL-TFH to AITL. The median number of morphologic features of AITL also correlated significantly with number of TFH markers positive (Spearman coefficient ρ=0.759). In summary, the stain panel chosen will have an impact on cases classified as PTCL-TFH. This entity may exist along a spectrum between PTCL-NOS and AITL.

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.

Proteomic profiling identifies outcome-predictive markers in patients with peripheral T-cell lymphoma, not otherwise specified

Peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) constitutes a heterogeneous category of lymphomas, which do not fit into any of the specifically defined T-cell lymphoma entities. Both the pathogenesis and tumor biology in PTCL-NOS are poorly understood. Protein expression in pretherapeutic PTCL-NOS tumors was analyzed by proteomics. Differentially expressed proteins were compared in 3 distinct scenarios: (A) PTCL-NOS tumor tissue (n = 18) vs benign lymphoid tissue (n = 8), (B) clusters defined by principal component analysis (PCA), and (C) tumors from patients with chemosensitive vs refractory PTCL-NOS. Selected differentially expressed proteins identified by proteomics were correlated with clinico-pathological features and outcome in a larger cohort of patients with PTCL-NOS (n = 87) by immunohistochemistry (IHC). Most proteins with altered expression were identified comparing PTCL-NOS vs benign lymphoid tissue. PCA of the protein profile defined 3 distinct clusters. All benign samples clustered together, whereas PTCL-NOS tumors separated into 2 clusters with different patient overall survival rates (P = .001). Differentially expressed proteins reflected large biological diversity among PTCL-NOS, particularly associated with alterations of "immunological" pathways. The 2 PTCL-NOS subclusters defined by PCA showed disturbance of "stress-related" and "protein metabolic" pathways. α-Enolase 1 (ENO1) was found differentially expressed in all 3 analyses, and high intratumoral ENO1 expression evaluated by IHC correlated with poor outcome (hazard ratio, 2.09; 95% confidence interval, 1.17-3.73; P = .013). High expression of triosephosphate isomerase (TPI1) also showed a tendency to correlate with poor survival (P = .057). In conclusion, proteomic profiling of PTCL-NOS provided evidence of markedly altered protein expression and identified ENO1 as a novel potential prognostic marker.

PD-1 Tumor Suppressor Signaling in T Cell Lymphomas

The inhibitory receptor PD-1 is critical to balancing antigen-induced T cell activation; its inhibition is currently being explored to enhance antitumor T cell immunity with certain successful outcomes. However, PD-1 has also emerged as a central tumor suppressor in T cell lymphomas, where the tumor cell originates from a T cell itself. These aggressive cancers are frequently characterized by oncogenic mutations in T cell receptor (TCR) signaling pathways. PD-1 activity within malignant T cells can negatively regulate the PI3K/AKT and PKCθ/NF-κB tumor survival pathways and PD-1 is frequently inactivated in this human malignancy. This review summarizes current insights into oncogenic T cell signaling, discusses tumor-suppressive functions and mechanisms of PD-1 in T cell lymphomagenesis, and addresses potential unwanted effects caused by PD-1 checkpoint inhibition.

Epidemiology and Pathology of T- and NK-Cell Lymphomas

PURPOSE

This review will describe and update readers on the recent changes in the 2017 WHO classification regarding peripheral T-cell lymphomas.

RECENT FINDINGS

Signficant advances in molecular studies have resulted in revisions to the classification as well as introduction to provisional entities such as breast implant-associated ALCL and nodal PTCL with T-follicular helper phenotype.

SUMMARY

Major advances in molecular and gene expression profiling has expanded our knowledge of these rare and aggressive diseases.

Characteristic Histological Findings of Asymptomatic EBV-associated Lymphoproliferative Disorders in Tonsils

Recently, an in situ hybridization (ISH) and immunohistochemical study demonstrated that Epstein-Barr virus (EBV) infection may be involved in tonsillar hypertrophy and recurrent tonsillitis in children and young adolescents. The present study was based on 630 consecutive specimens from tonsillectomies performed at the Dokkyo University School of Medicine between 2002 and May 2017. Clinical findings were obtained from hospital records. Histologically, a “pale clear zone” was characterized by hyperplastic germinal centers with ill-defined borders and interfollicular expansion. Immunohistologically, the majority of immunoblasts were CD20-positive, whereas medium to large lymphoid cells usually expressed CD3. Among 14 lesions, numerous EBV-encoded small RNA (EBER)-positive cells were detected in 10. In 7 of these 10 lesions, EBER-positive cells were detected in germinal centers as well as in the interfollicular area. Based on our results, the “pale clear zone” suggests asymptomatic EBV infection of the tonsil. The present study demonstrated that “pale clear zones” should be taken into consideration when diagnosing asymptomatic EBV-associated LPDs in the tonsils of children and young adolescents as well as in middle-aged patients.

Overlap at the molecular and immunohistochemical levels between angioimmunoblastic T-cell lymphoma and a subgroup of peripheral T-cell lymphomas without specific morphological features

The overlap of morphology and immunophenotype between angioimmunoblastic T-cell lymphoma (AITL) and other nodal peripheral T-cell lymphomas (n-PTCLs) is a matter of current interest whose clinical relevance and pathogenic background have not been fully established. We studied a series of 98 n-PTCL samples (comprising 57 AITL and 41 PTCL-NOS) with five T_FH antibodies (CD10, BCL-6, PD-1, CXCL13, ICOS), looked for mutations in five of the genes most frequently mutated in AITL (TET2, DNMT3A, IDH2, RHOA and PLCG1) using the Next-Generation-Sequencing Ion Torrent platform, and measured the correlations of these characteristics with morphology and clinical features. The percentage of mutations in the RHOA and TET2 genes was similar (23.5% of cases). PLCG1 was mutated in 14.3%, IDH2 in 11.2% and DNMT3A in 7.1% of cases, respectively. In the complete series, mutations in RHOA gene were associated with the presence of mutations in IDH2, TET2 and DNMT3A (p < 0.001, p = 0.043, and p = 0.029, respectively). Fourteen cases featured RHOA mutations without TET2 mutations. A close relationship was found between the presence of these mutations and a T_FH-phenotype in AITL and PTCL-NOS patients. Interestingly, BCL-6 expression was the only T_FH marker differentially expressed between AITL and PTCL-NOS cases. There were many fewer mutated cases than there were cases with a T_FH phenotype. Overall, these data suggest alternative ways by which neoplastic T-cells overexpress these proteins. On the other hand, no clinical or survival differences were found between any of the recognized subgroups of patients with respect to their immunohistochemistry or mutational profile.

Clinicopathological Study of 30 Cases of Peripheral T-cell Lymphoma with Hodgkin and Reed-Sternberg-like B-cells from Japan

The presence of Hodgkin and Reed-Sternberg (HRS)-like B-cells in peripheral T-cell lymphoma (PTCL) is rare and its clinicopathological features still remain unclear. Here, we describe 30 cases of PTCL with HRS-like B-cells from Japan. Twenty-three cases (77%) presented evidence of follicular T-helper phenotype (TFH) derivation: 12 were angioimmunoblastic T-cell lymphoma and 11 PTCL with TFH phenotype (PTCL-TFH). The remaining seven cases were diagnosed as PTCL, not otherwise specified (PTCL-NOS). Epstein-Barr virus (EBV) reactivation was detected in 25 cases (83%), but HRS-like B-cells were EBER in only 20 cases (67%). The median age at diagnosis was 77 years (range, 39-91 y), including 24 patients (80%) were older than 60 years of age. Most of the patients presented at an advanced clinical stage and were associated with higher risk according to the International Prognostic Index. The 3-year overall and progression-free survival rates were 44% and 27%, respectively. No significant clinicopathological differences were detected between PTCL-TFH, PTCL-NOS and the angioimmunoblastic cases. Cases with EBER HRS-like B-cells were associated with inferior overall and progression-free survival compared to those with EBER HRS-like B-cells, but the difference was not significant. In conclusion, HRS-like B-cells were found in a subset of T-cell lymphomas, especially in association with the TFH phenotype and EBV reactivation. These cells have a tendency to affect elderly patients and to be associated with advanced clinical stages and dismal prognosis. The EBV status of HRS-like B-cells does not seem to affect the clinicopathological features of this group of PTCLs.

Follicular helper T-cell-related lymphomas

In this issue of Blood, Wang et al describe the occurrence and pathogenetic relevance of IDH2R172 mutations in angioimmunoblastic T-cell lymphoma (AITL).

Peripheral T-cell and NK cell lymphoproliferative disorders: cell of origin, clinical and pathological implications

T-cell lymphoproliferative disorders are a heterogeneous group of neoplasms with distinct clinical-biological properties. The normal cellular counterpart of these processes has been postulated based on functional and immunophenotypic analyses. However, T lymphocytes have been proven to be remarkably capable of modulating their properties, adapting their function in relationship with multiple stimuli and to the microenvironment. This impressive plasticity is determined by the equilibrium among a pool of transcription factors and by DNA chromatin regulators. It is now proven that the acquisition of specific genomic defects leads to the enforcement/activation of distinct pathways, which ultimately alter the preferential activation of defined regulators, forcing the neoplastic cells to acquire features and phenotypes distant from their original fate. Thus, dissecting the landscape of the genetic defects and their functional consequences in T-cell neoplasms is critical not only to pinpoint the origin of these tumors but also to define innovative mechanisms to re-adjust an unbalanced state to which the tumor cells have become addicted and make them vulnerable to therapies and targetable by the immune system. In our review, we briefly describe the pathological and clinical aspects of the T-cell lymphoma subtypes as well as NK-cell lymphomas and then focus on the current understanding of their pathogenesis and the implications on diagnosis and treatment.

Past, present and future treatment strategies in peripheral T-cell lymphomas

SUMMARY 

Nodal peripheral T-cell lymphomas (PTCLs) are very aggressive tumors characterized by poor response to conventional chemotherapy and dismal prognosis. Recent evidence has indicated that, at least for patients aged less than 60 years, frontline high-dose chemotherapy followed by autologous stem cell transplantation can be an effective strategy. Unfortunately, however, a significant fraction of patients cannot benefit from this approach, due to age, poor performance status or early relapse. In addition, a percentage of transplanted patients eventually relapse. In this article, based on their experience and on the most recent literature, the authors review the current concept on PTCL treatment, focusing on the most common PTCL nodal subtypes.

Clonal identity and histologic difference in peripheral T-cell lymphoma with follicular helper T-cell phenotype simultaneously occurring at common bile duct and lymph nodes

We present the first case of peripheral T-cell lymphoma, not otherwise specified expressing follicular helper T-cell markers with different histologic features simultaneously involving the common bile duct and pericholedochal lymph nodes in a 72-year-old woman patient. Abdominal computed tomography revealed a localized wall thickening in the common bile duct. With the impression of cholangiocarcinoma, pancreaticoduodenectomy was done. Microscopically, dense small lymphoid cells with only minimal cytologic atypia were observed with occasional lymphoepithelial-like lesions, whereas many atypical large cells infiltrated the pericholedochal lymph nodes. Immunohistochemically, most small cells in the bile duct and the large atypical cells in the lymph nodes were all reactive for follicular helper T-cell markers including CD4, PD-1, and CXCL-13. BIOMED-2 based polymerase chain reaction using the DNA template from either the bile duct lesion or the lymph node revealed identical but different dominant clonal peaks, indicating these 2 lesions represent a spectrum of the same disease.

Peripheral T-cell lymphomas of follicular T-helper cell derivation with Hodgkin/Reed-Sternberg cells of B-cell lineage: both EBV-positive and EBV-negative variants exist

Peripheral T-cell lymphomas (PTCLs) are functionally and morphologically complex. Epstein-Barr virus (EBV)-positive B cells have been reported in angioimmunoblastic T-cell lymphoma (AITL) and other PTCLs and may mimic Hodgkin/Reed-Sternberg (HRS) cells, but EBV-negative HRS-like B cells have not been described. We wished to assess the nature of the PTCL associated with HRS-like cells and to determine whether EBV-negative HRS-like cells may be seen. We identified 57 PTCL cases reported as containing HRS-like cells. These included 32 AITL, 19 PTCL, not otherwise specified (NOS), 3 PTCL-NOS, follicular variant, 1 PTCL-NOS, T-zone variant, and 2 adult T-cell leukemia/lymphoma cases. All patients were adults with a median age of 63 and presented with lymphadenopathy. The male:female ratio was 31:26 (1.2:1). Clonal TRG rearrangement was detected in 46/53 cases. Six of 38 cases had a concomitant clonal immunoglobulin gene rearrangement. In 52/57 cases the HRS cells were positive for EBV. Five cases, 3 classified as AITL and 2 as PTCL-NOS, follicular variant, contained HRS-like cells negative for EBV. All PTCLs with EBV-negative HRS cells had a T follicular helper cell immunophenotype. The neoplastic T cells expressed CD3, CD4, and PD-1 and formed rosettes around the HRS-like cells. The HRS-like cells were positive for CD20 (variable intensity), PAX5, CD30, and CD15 (4/5). We conclude that both EBV-positive and EBV-negative HRS-like B cells may occur in the background of PTCL; caution is needed to avoid misdiagnosis as classical Hodgkin lymphoma. The close interaction between the HRS-like cells and the rosetting PD-1-positive T cells suggests a possible pathogenetic role in this phenomenon and provides new insights into the abnormal B-cell proliferations that occur in the context of TFH malignancies.

Molecular profiling improves classification and prognostication of nodal peripheral T-cell lymphomas: results of a phase III diagnostic accuracy study

PURPOSE

The differential diagnosis among the commonest peripheral T-cell lymphomas (PTCLs; ie, PTCL not otherwise specified [NOS], angioimmunoblastic T-cell lymphoma [AITL], and anaplastic large-cell lymphoma [ALCL]) is difficult, with the morphologic and phenotypic features largely overlapping. We performed a phase III diagnostic accuracy study to test the ability of gene expression profiles (GEPs; index test) to identify PTCL subtype.

METHODS

We studied 244 PTCLs, including 158 PTCLs NOS, 63 AITLs, and 23 ALK-negative ALCLs. The GEP-based classification method was established on a support vector machine algorithm, and the reference standard was an expert pathologic diagnosis according to WHO classification.

RESULTS

First, we identified molecular signatures (molecular classifier [MC]) discriminating either AITL and ALK-negative ALCL from PTCL NOS in a training set. Of note, the MC was developed in formalin-fixed paraffin-embedded (FFPE) samples and validated in both FFPE and frozen tissues. Second, we found that the overall accuracy of the MC was remarkable: 98% to 77% for AITL and 98% to 93% for ALK-negative ALCL in test and validation sets of patient cases, respectively. Furthermore, we found that the MC significantly improved the prognostic stratification of patients with PTCL. Particularly, it enhanced the distinction of ALK-negative ALCL from PTCL NOS, especially from some CD30+ PTCL NOS with uncertain morphology. Finally, MC discriminated some T-follicular helper (Tfh) PTCL NOS from AITL, providing further evidence that a group of PTCLs NOS shares a Tfh derivation with but is distinct from AITL.

CONCLUSION

Our findings support the usage of an MC as additional tool in the diagnostic workup of nodal PTCL.

[Nodular lymphocyte-predominant Hodgkin's lymphoma and differential diagnoses]

Nodular lymphocyte-predominant Hodgkin's lymphoma (NLPHL) is a rare subtype of Hodgkin's lymphoma. The histological patterns of NLPHL variants are characterized by different localizations of the tumor cells, intranodular and perinodular and by the varying composition of the microenvironment. T-cell/histiocyte-rich B-cell lymphoma may be the result of an aggressive transformation of NLPHL. Classical lymphocyte-rich Hodgkin's lymphoma can usually be clearly distinguished from NLPHL by the immunophenotype of the tumor cells. Further differential diagnoses include follicular lymphoma and the follicular variant of peripheral T-cell lymphoma. Angioimmunoblastic T-cell lymphoma with CD20-positive blasts represents a differential diagnosis to the diffuse variants of NLPHL.

Pathobiology of T-cell and NK-cell lymphomas

T-cell and NK-cell lymphomas are uncommon lymphomas with an aggressive clinical course. The causes and precise cellular origins of most T-cell lymphomas are still not well defined. The WHO classification utilizes morphologic and immunophenotypic features in conjunction with clinical aspects and in some instances genetics to delineate a prognostically and therapeutically meaningful categorization. The anatomic localization of neoplastic T-cells and NK-cells parallels in part their proposed normal cellular counterparts and functions. T-cells of the adaptive immune system are mainly based in lymph nodes and peripheral blood, whereas lymphomas derived from T-cells and NK-cells of the innate immune system are mainly extranodal. This approach allows for better understanding of some of the manifestations of the T-cell and NK-cell lymphomas, including their cellular distribution, some aspects of morphology and even associated clinical findings.

ESMO Consensus conferences: guidelines on malignant lymphoma. part 2: marginal zone lymphoma, mantle cell lymphoma, peripheral T-cell lymphoma

To complement the existing treatment guidelines for all tumour types, ESMO organizes consensus conferences to focus on specific issues in each type of tumour. In this setting, a consensus conference on the management of lymphoma was held on 18 June 2011 in Lugano, next to the 11th International Conference on Malignant Lymphoma. The conference convened ∼30 experts from all around Europe, and selected six lymphoma entities to be addressed; for each of them, three to five open questions were to be addressed by the experts. For each question, a recommendation should be given by the panel, referring to the strength of the recommendation based on the level of evidence. This consensus report focuses on the three less common lymphoproliferative malignancies: marginal zone lymphoma, mantle cell lymphoma, and peripheral T-cell lymphomas. A first report had focused on diffuse large B-cell lymphoma, follicular lymphoma, and chronic lymphocytic leukaemia.

Peripheral T-cell and NK-cell lymphomas in the WHO classification: pearls and pitfalls

Peripheral T-cell and NK-cell lymphomas are functionally, pathologically, and clinically complex. Most nodal T-cell lymphomas belong to the adaptive immune system, whereas many extranodal T-cell and NK-cell lymphomas are derived from innate immune cells. The pathological manifestations often reflect the functional attributes of the neoplastic cells. Several forms of peripheral T-cell lymphoma are derived from T-follicular helper cells (T(FH)), and include angioimmunoblastic T-cell lymphoma, the follicular variant of peripheral T-cell lymphoma, not otherwise specified, and primary cutaneous small/medium CD4-positive T-cell lymphoma. T(FH)-derived neoplasms are often associated with atypical and clonal B-cell proliferations, which take a number of forms, sometimes mimicking classical Hodgkin's lymphoma, and sometimes showing marked plasmacytic differentiation. Most extranodal T-cell lymphomas are cytotoxic and often arise in mucosal-associated sites. They can be derived from either αβ or γδ cytotoxic T cells, and include subcutaneous panniculitis-like T-cell lymphoma, and enteropathy-associated T-cell lymphomas, both Type I and Type II. Type I enteropathy-associated lymphomas occur in association with celiac disease, whereas Type II lymphomas are more often sporadic. For some T-cell lymphomas, such as hepatosplenic T-cell lymphoma, immunophenotypic heterogeneity is seen within a single disease entity. New data are emerging on the molecular pathogenesis of T-cell and NK-cell lymphoma, but most tumor types remain poorly characterized.

Follicular T-cell lymphoma: a member of an emerging family of follicular helper T-cell derived T-cell lymphomas

Unlike B-cell lymphomas, where knowledge of normal B-cell origin and differentiation has greatly contributed to their classification, the current classification of peripheral T-cell lymphomas is limited by a lack of understanding of their cellular origin. In the current World Health Organization classification of lymphomas, follicular T-cell lymphoma was formally recognized as a morphologic variant of peripheral T-cell lymphoma, not otherwise specified. There is growing evidence, however, that follicular T-cell lymphoma may be a unique clinicopathologic entity based on its morphologic features and derivation from follicular helper T-cells. In addition, there are abundant recent data supporting the concept that follicular helper T-cells can give rise to other types of T-cell lymphoma, including angioimmunoblastic T-cell lymphoma, primary cutaneous CD4+ small/medium T-cell lymphoma, and a subset of neoplasms, in addition to follicular T-cell lymphoma, currently classified as peripheral T-cell lymphoma, not otherwise specified. In this review, we focus primarily on the clinicopathologic, immunophenotypic, and molecular features of follicular T-cell lymphoma and discuss its potential relationship with other types of T-cell lymphoma thought to be derived from follicular helper T-cells.

New molecular insights into peripheral T cell lymphomas

Peripheral T cell lymphomas (PTCLs) are heterogeneous neoplasms and represent about 12% of all lymphoid malignancies. They are often regarded as "orphan diseases," a designation that does not reflect their real incidence but rather signifies the difficulties encountered in their classification, diagnosis, and treatment. Here we revise the current understanding of the pathobiological characteristics of the most common nodal PTCLs by focusing on the contribution given by high-throughput technologies and the identification of potential therapeutic targets proposed by translational studies.

Revising the historical collection of epithelioid cell-rich lymphomas of the Kiel Lymph Node Registry: what is Lennert's lymphoma nowadays?

AIMS

Lennert's lymphoma is a rare variant of peripheral T-cell lymphoma (PTCL) not otherwise specified (NOS). The aim of this study was to further characterize this tumour.

METHODS AND RESULTS

Historical material of 97 lymphomas with a high content of epithelioid cells, collected at the Kiel Lymph Node Registry were reviewed, by applying immunohistochemistry and current diagnostic criteria. Among all cases revised, various B-cell lymphoma entities (25 cases), Hodgkin lymphomas (21 cases) and PTCL subtypes (48 cases) could be identified. A distinctive subgroup of eight PTCLs was found that were regarded as genuine Lennert's lymphomas. These cases were characterized by mild atypia, a non-activated cytotoxic phenotype [TIA1 cytotoxic granule-associated RNA binding protein (TIA1)-positive(+) and granzyme B-negative], and a substantial lack of follicular T-helper (T(FH) ) cell markers. Among the other PTCLs, including angioimmunoblastic T-cell lymphoma and PTCL NOS, many cases with positivity for more than three T(FH) cell-associated molecules were recorded.

CONCLUSIONS

Our study shows that, according to current criteria, Lennert's lymphoma is a rare but distinctive entity among epithelioid cell-rich lymphomas, differing on grounds of morphology and immunophenotype from other PTCL subtypes. An additional finding is the broad morphological spectrum of epithelioid-cell rich PTCLs showing a T(FH) cell phenotype.