Dependence on mitochondrial respiration of malignant T cells reveals a new therapeutic target for angioimmunoblastic T-cell lymphoma.

Cancer metabolic reprogramming has been recognized as one of the cancer hallmarks that promote cell proliferation, survival, as well as therapeutic resistance. Up-to-date regulation of metabolism in T-cell lymphoma is poorly understood. In particular, for human angioimmunoblastic T-cell lymphoma (AITL) the metabolic profile is not known. Metabolic intervention could help identify new treatment options for this cancer with very poor outcomes and no effective medication. Transcriptomic analysis of AITL tumor cells, identified that these cells use preferentially mitochondrial metabolism. By using our preclinical AITL mouse model, mimicking closely human AITL features, we confirmed that T follicular helper (Tfh) tumor cells exhibit a strong enrichment of mitochondrial metabolic signatures. Consistent with these results, disruption of mitochondrial metabolism using metformin or a mitochondrial complex I inhibitor such as IACS improved the survival of AITL lymphoma-bearing mice. Additionally, we confirmed a selective elimination of the malignant human AITL T cells in patient biopsies upon mitochondrial respiration inhibition. Moreover, we confirmed that diabetic patients suffering from T-cell lymphoma, treated with metformin survived longer as compared to patients receiving alternative treatments. Taking together, our findings suggest that targeting the mitochondrial metabolic pathway could be a clinically efficient approach to inhibit aggressive cancers such as peripheral T-cell lymphoma.

A practical approach to the modern diagnosis and classification of T-and NK-cell lymphomas.

T- and NK-cell lymphomas are neoplasms derived from immature T cells (lymphoblastic lymphomas), or more commonly, from mature T and NK cells (peripheral T-cell lymphomas, PTCLs). PTCLs are rare but show marked biologic and clinical diversity. They are usually aggressive and may present in lymph nodes, blood, bone marrow or other organs. More than 30 T/NK-cell derived neoplastic entities are recognized in the International Consensus Classification and the classification of the World Health Organization (5th edition), both published in 2022, which integrate most recent knowledge in hematology, immunology, pathology and genetics. In both proposals, disease definition aims to integrate clinical features, etiology, implied cell of origin, morphology, phenotype and genetic features into biologically and clinically relevant clinico-pathologic entities. Cell derivation from innate immune cells, or specific functional subsets of CD4+ T cells like follicular helper T cells, are major determinants delineating entities. Accurate diagnosis of T/NK-cell lymphoma is essential for clinical management and mostly relies on tissue biopsies. Because the histologic presentation may be heterogeneous and overlaps with that of many benign lymphoid proliferations and B-cell lymphomas, the diagnosis is often challenging. Disease location, morphology and immunophenotyping remain the main features guiding the diagnosis, often complemented by genetic analysis including clonality and high-throughput sequencing mutational studies. This review provides a comprehensive overview of the classification and diagnosis of T-cell lymphoma in the context of current concepts and scientific knowledge.

Deep phenotyping of nodal T-cell lymphomas reveals immune alterations and therapeutic targets.

Whereas immunotherapies have revolutionized the treatment of different solid and hematological cancers, their efficacy in nodal peripheral T-cell lymphomas (PTCLs) is limited, due to a lack of understanding of the immune response they trigger. To fully characterize the immune tumor microenvironment (TME) of PTCLs, we performed spectral flow cytometry analyses on 11 angioimmunoblastic T-cell lymphomas (AITL), 7 PTCL, not otherwise specified (PTCL, NOS) lymph node samples, and 10 non-tumoral control samples. The PTCL TME contained a larger proportion of regulatory T cells and exhausted CD8+ T cells, with enriched expression of druggable immune checkpoints. Interestingly, CD39 expression was up-regulated at the surface of most immune cells, and a multi-immunofluorescence analyses on a retrospective cohort of 43 AITL patients demonstrated a significant association between high CD39 expression by T cells and poor patient prognosis. Together, our study unravels the complex TME of nodal PTCLs, identifies targetable immune checkpoints, and highlights CD39 as a novel prognostic factor.

Oral azacitidine compared with standard therapy in patients with relapsed or refractory follicular helper T-cell lymphoma (ORACLE): an open-label randomised, phase 3 study.

BACKGROUND: Follicular helper T-cell lymphomas (TFHL) harbour frequent alterations in genes that regulate DNA methylation. Preliminary reports suggest that treatment with 5-azacitidine has clinical activity in patients with relapsed or refractory TFHL. We aimed to compare the oral form of azacitidine with investigator's choice standard therapy (ICT; ie, gemcitabine, bendamustine, or romidepsin) in patients with relapsed or refractory TFHL. METHODS: Patients older than 18 years with relapsed or refractory TFHL (angioimmunoblastic T-cell lymphoma, follicular lymphoma, or nodal T-cell lymphoma with phenotype, ie, positive with two or more markers among CD10, BCL6, CXCL13, PD1, or ICOS) based on the 2017 WHO classification of haematological neoplasms, with an Eastern Cooperative Oncology Group performance status score of 0-3, were recruited in university hospitals from five European countries and from Japan. Patients were randomly assigned 1:1 to treatment with either azacitidine given at a dose of 300 mg once a day (200 mg in Japanese patients) for 14 days in a 28-day cycle or gemcitabine, bendamustine, or romidepsin according to the investigator's choice. Random assignment was stratified by the number of previous lines of therapy and by the presence of previous or concomitant myeloid malignancy. The primary endpoint was investigator-assessed progression-free survival, presented in the intention-to-treat population. This Article is the final analysis of this trial, registered at ClinicalTrials.gov (Europe NCT03593018 and Japan NCT03703375). FINDINGS: 86 patients (median age 69 years [IQR 62-76], 50 patients were male, 36 were female) were enrolled between Nov 9, 2018, to Feb 22, 2021; 42 in the azacitidine group and 44 in the ICT group. With a median follow-up of 27·4 months (IQR 20·2-32·9), the median progression-free survival was 5·6 months (95% CI 2·7 -8·1) in the azacitidine group versus 2·8 months (1·9-4·8) in the ICT group (hazard ratio of 0·63 (95% CI 0·38-1·07); 1-sided p=0·042). Grade 3-4 adverse events were reported in 32 (76%) of 42 patients in the azacitidine group versus 42 (98%) of 43 patients in the ICT group. The most adverse grade 3 or worse adverse events were haematological (28 [67%] of 42 patients vs 40 [93%] of 43 patients), infection (8 [19%] and 14 [33%]), and gastrointestinal (5 [12%] vs 1 [2%] for azacitidine and ICT, respectively). There were two treatment-related deaths in the azacitidine group (one endocarditis and one candidiasis) and three in the ICT group (one heart failure, one COVID-19, and one cause unknown). INTERPRETATION: Although the pre-specified primary outcome of the trial was not met, the favourable safety profile suggests that azacitidine could add to the treatment options in these difficult to treat diseases especially in combination with other drugs. Trials with combination are in preparation in a platform trial. FUNDING: Bristol-Myers Squibb. TRANSLATION: For the French translation of the abstract see Supplementary Materials section.

Romidepsin Plus Cyclophosphamide, Doxorubicin, Vincristine, and Prednisone Versus Cyclophosphamide, Doxorubicin, Vincristine, and Prednisone in Patients With Previously Untreated Peripheral T-Cell Lymphoma: Final Analysis of the Ro-CHOP Trial.

Clinical trials frequently include multiple end points that mature at different times. The initial report, typically based on the primary end point, may be published when key planned co-primary or secondary analyses are not yet available. Clinical Trial Updates provide an opportunity to disseminate additional results from studies, published in JCO or elsewhere, for which the primary end point has already been reported.The primary analysis of the Ro-CHOP phase III randomized controlled trial (ClinicalTrials.gov identifier: NCT01796002) established that romidepsin (Ro) plus cyclophosphamide, doxorubicin, vincristine, prednisone (CHOP) did not yield an increased efficacy compared with CHOP alone as first-line treatment of peripheral T-cell lymphoma. We report the planned final analysis 5 years after the last patient enrolled. With a median follow-up of 6 years, median progression-free survival (PFS) was 12.0 months compared with 10.2 months (hazard ratio [HR], 0.79 [95% CI, 0.62 to 1.005]; P = .054), while median overall survival was 62.2 months (35.7-86.6 months) and 43.8 months (30.1-70.2 months; HR, 0.88 [95% CI, 0.68 to 1.14]; P = .324) in the Ro-CHOP and CHOP arms, respectively. In an exploratory analysis, the median PFS in the centrally reviewed follicular helper T-cell lymphoma subgroup was significantly longer in the Ro-CHOP arm (19.5 v 10.6 months, HR, 0.703 [95% CI, 0.502 to 0.985]; P = .039). Second-line treatments were given to 251 patients with a median PFS2 and OS2 after relapse or progression of 3.3 months and 11.5 months, respectively. Within the limits of highly heterogeneous second-line treatments, no specific regimen seemed to provide superior disease control. However, a potential benefit was observed with brentuximab vedotin in association with chemotherapy even after excluding anaplastic large-cell lymphoma subtype or after adjusting for histology and international prognostic index in a multivariate model (HR for PFS, 0.431 [95% CI, 0.238 to 0.779]; P = .005).

Inhibition of choline metabolism in an angioimmunoblastic T-cell lymphoma preclinical model reveals a new metabolic vulnerability as possible target for treatment.

BACKGROUND: Angioimmunoblastic T-cell lymphoma (AITL) is a malignancy with very poor survival outcome, in urgent need of more specific therapeutic strategies. The drivers of malignancy in this disease are CD4+ follicular helper T cells (Tfh). The metabolism of these malignant Tfh cells was not yet elucidated. Therefore, we decided to identify their metabolic requirements with the objective to propose a novel therapeutic option. METHODS: To reveal the prominent metabolic pathways used by the AITL lymphoma cells, we relied on metabolomic and proteomic analysis of murine AITL (mAITL) T cells isolated from our established mAITL model. We confirmed these results using AITL patient and healthy T cell expression data. RESULTS: Strikingly, the mAITL Tfh cells were highly dependent on the second branch of the Kennedy pathway, the choline lipid pathway, responsible for the production of the major membrane constituent phosphatidylcholine. Moreover, gene expression data from Tfh cells isolated from AITL patient tumors, confirmed the upregulation of the choline lipid pathway. Several enzymes involved in this pathway such as choline kinase, catalyzing the first step in the phosphatidylcholine pathway, are upregulated in multiple tumors other than AITL. Here we showed that treatment of our mAITL preclinical mouse model with a fatty acid oxydation inhibitor, significantly increased their survival and even reverted the exhausted CD8 T cells in the tumor into potent cytotoxic anti-tumor cells. Specific inhibition of Chokα confirmed the importance of the phosphatidylcholine production pathway in neoplastic CD4 + T cells, nearly eradicating mAITL Tfh cells from the tumors. Finally, the same inhibitor induced in human AITL lymphoma biopsies cell death of the majority of the hAITL PD-1high neoplastic cells. CONCLUSION: Our results suggest that interfering with choline metabolism in AITL reveals a specific metabolic vulnerability and might represent a new therapeutic strategy for these patients.

Angioimmunoblastic T-cell lymphoma and Kaposi sarcoma: A fortuitous collision?

AIMS: Follicular helper T-cell (TFH) lymphoma of the angioimmunoblastic-type (AITL), one of the most prevalent T-cell lymphomas, typically encompasses proliferation of high endothelial venules and Epstein-Barr virus-positive immunoblasts, but neither infection with HHV8 nor association with Kaposi's sarcoma (KS) have been described. The aims of this study are to characterise the association between AITL and HHV8 infection or KS. METHODS AND RESULTS: Three male patients aged 49-76 years, HIV-negative, with concurrent nodal involvement by AITL and KS, were identified from our files and carefully studied. Two patients originated from countries where endemic KS occurs, including one with cutaneous KS. The lymphomas featured abundant vessels, expanded follicular dendritic cells and neoplastic TFH cells [PD1+ (three of three), ICOS+ (three of three), CXCL13+ (three of three), CD10+ (two of three), BCL6 (two of three)] but lacked EBV+ immunoblasts. The foci of KS consisted of subcapsular proliferations of ERG+, CD31+ and/or CD34+ , HHV8+ spindle cells. High-throughput sequencing showed AITL-associated mutations in TET2 (three of three), RHOA (G17V) (three of three) and IDH2 (R172) (two of three), which were absent in the microdissected KS component in two cases. Relapses in two patients consisted of AITL, without evidence of KS. No evidence of HHV8 infection was found in a control group of 23 AITL cases. CONCLUSION: Concurrent nodal involvement by AITL and KS is rare and identification of both neoplastic components may pose diagnostic challenges. The question of whether the association between AITL and KS may be fortuitous or could reflect the underlying immune dysfunction in AITL remains open.

Clinical and histological study of follicular helper T-cell lymphomas with indolent evolution.

INTRODUCTION: Follicular helper T-cell lymphomas (TFHL) have an aggressive course with a poor outcome. European and US guidelines recommend anthracycline-based chemotherapy as a first-line treatment, but the 5-year overall survival rate is still approximately 30%. We describe here the features of a cohort of TFHL patients who experienced prolonged survival despite the absence of specific treatment or the initiation of steroid-based therapy. PATIENTS AND METHODS: In our study, we describe 15 adult patients who suffered from TFHL and had not received intensive chemotherapy at diagnosis for any reason. Biopsies of these cases were centrally reviewed, and the mutational pattern was determined using next-generation sequencing. RESULTS: These 15 patients had the classic clinical, biological and pathological features of TFHL, angioimmunoblastic-type. TET2 mutations were found in 83% of patients; RHOA G17V, IDH2 R172 and DNMT3A mutations were found in 67%, 42% and 33% of the patients, respectively. Among the 15 patients, 8 did not receive any treatment, and 7 received steroid-based treatment. Ten patients had progression (5 in each group). Four patients died (3 of them from the progression of their lymphoma). The median follow-up in our cohort was 53 months. The 5-year OS was 66%, 100% for untreated patients and 29% for the others. In those 2 groups, the median time to treatment initiation was 22 months from diagnosis. CONCLUSION: We described a series of 15 well-characterized TFHL patients with an indolent outcome, suggesting that a watch-and-wait approach can be proposed in selected patients. Identifying factors predicting such evolution is warranted.

High PDL1/PDL2 gene expression correlates with worse outcome in primary mediastinal large B-cell lymphoma.

Primary mediastinal B-cell lymphoma (PMBL) is an uncommon entity of aggressive B-cell lymphoma with an unusually good prognosis, except for 10-15% of chemotherapy-refractory cases. To identify earlier these higher risk patients, we performed molecular characterization of a retrospective multicenter cohort of patients treated with firstline immunochemotherapy. The traits of the patients with gene-expression profiling data (n = 120) were as follows: median age of 34 years (range, 18-67 years); female sex, 58.3%; elevated lactate dehydrogenase, 82.5%; Eastern Cooperative Oncology Group performance status score of 0 to 1, 85.7%; Ann Arbor stage I/II, 55%; International Prognostic Index score of 1 to 2, 64.4%; and median metabolic tumor volume, 290.4 cm3 (range, 15.7-1147.5 cm3). Among all 137 markers tested for correlation with survival data, only programmed death-ligand (PDL) 1 and PDL2 expression showed a prognostic impact. Overall, both PDL1 and PDL2 genes were highly expressed in 37 patients (30.8%; PDL1high/PDL2high). The baseline clinical characteristics of patients with PDL1high/PDL2high were similar to those of other patients. In univariate analysis, PDL1high/PDL2high status was associated with poor progression-free survival (PFS) (hazard ratio [HR], 4.292) and overall survival (OS; HR, 8.24). In multivariate analysis, PDL1high/PDL2high status was an independent prognostic factor of adverse outcomes (PFS: HR, 5.22; OS: HR, 10.368). We validated these results in an independent cohort of 40 patients and confirmed the significant association between PDL1high/PDL2high status and inferior PFS (HR, 6.11). High PDL1/PDL2 gene expression defines a population with strong immune privilege and poorer outcomes from standard chemotherapy who might benefit from firstline checkpoint inhibitor therapy.

How molecular advances may improve the diagnosis and management of PTCL patients.

Peripheral T-cell lymphomas (PTCL) comprised more than 30 rare heterogeneous entities, representing 10 to 15% of adult non-Hodgkin lymphomas. Although their diagnosis is still mainly based on clinical, pathological, and phenotypic features, molecular studies have allowed for a better understanding of the oncogenic mechanisms involved and the refinement of many PTCL entities in the recently updated classifications. The prognosis remains poor for most entities (5-year overall survival < 30%), with current conventional therapies based on anthracyclin-based polychemotherapy regimen, despite many years of clinical trials. The recent use of new targeted therapies appears to be promising for relapsed/refractory patients, such as demethylating agents in T-follicular helper (TFH) PTCL. However further studies are needed to evaluate the proper combination of these drugs in the setting of front-line therapy. In this review, we will summarize the oncogenic events for the main PTCL entities and report the molecular targets that have led to the development of new therapies. We will also discuss the development of innovative high throughput technologies that aid the routine workflow for the histopathological diagnosis and management of PTCL patients.

Baseline circulating tumour DNA and total metabolic tumour volume as early outcome predictors in aggressive large B-cell lymphoma. A real-world 112-patient cohort.

Approximately 20%-50% of patients with large B-cell lymphoma (LBCL) experience poor outcomes. We aimed to evaluate the combined prognostic value of circulating tumour DNA (ctDNA) and total metabolic tumour volume (TMTV) in LBCL. This observational single-centre study included 112 newly diagnosed LBCL patients, receiving R-CHOP/R-CHOP-like chemotherapies. CtDNA load was calculated following next-generation sequencing of cell-free DNA (cfDNA) using a targeted 40-gene lymphopanel. TMTV was measured using a fully automated artificial intelligence-based method for lymphoma lesion segmentation. CtDNA was detected in cfDNA samples from 95 patients with a median concentration of 3.15 log haploid genome equivalents per mL. TMTV measurements were available for 102 patients. The median TMTV was 501 mL. High ctDNA load (>3.57 log hGE/mL) or high TMTV (>200 mL) were associated with shorter 1-year PFS (44% vs. 83%, p < 0.001 and 64% vs. 97%, p = 0.002, respectively). When combined, three prognostic groups were identified. The shortest PFS was observed when both TMTV and ctDNA load were high (p < 0.001). Even with a short follow up, combining ctDNA load with TMTV improved the risk stratification of patients with aggressive LBCL. In the near future, very high-risk patients could benefit from CAR T-cell therapy or bispecific antibodies as first-line treatments.

Lack of reproducibility of histopathological features in MYC-rearranged large B cell lymphoma using digital whole slide images: a study from the Lunenburg lymphoma biomarker consortium.

AIMS: Subclassification of large B cell lymphoma (LBCL) is challenging due to the overlap in histopathological, immunophenotypical and genetic data. In particular, the criteria to separate diffuse large B cell lymphoma (DLBCL) and high-grade B cell lymphoma (HGBL) are difficult to apply in practice. The Lunenburg Lymphoma Biomarker Consortium previously reported a cohort of over 5000 LBCL that included fluorescence in-situ hybridisation (FISH) data. This cohort contained 209 cases with MYC rearrangement that were available for a validation study by a panel of eight expert haematopathologists of how various histopathological features are used. METHODS AND RESULTS: Digital whole slide images of haematoxylin and eosin-stained sections allowed the pathologists to visually score cases independently as well as participate in virtual joint review conferences. Standardised consensus guidelines were formulated for scoring histopathological features and included overall architecture/growth pattern, presence or absence of a starry-sky pattern, cell size, nuclear pleomorphism, nucleolar prominence and a range of cytological characteristics. Despite the use of consensus guidelines, the results show a high degree of discordance among the eight expert pathologists. Approximately 50% of the cases lacked a majority score, and this discordance spanned all six histopathological features. Moreover, none of the histological variables aided in prediction of MYC single versus double/triple-hit or immunoglobulin-partner FISH-based designations or clinical outcome measures. CONCLUSIONS: Our findings indicate that there are no specific conventional morphological parameters that help to subclassify MYC-rearranged LBCL or select cases for FISH analysis, and that incorporation of FISH data is essential for accurate classification and prognostication.

Lenalidomide maintenance fails to overcome the unfavourable prognosis of low NK-cell counts in rituximab-chemotherapy responsive elderly DLBCL patients: A LYSA group study.

Low baseline NK-cell counts (NKCCs) in patients with diffuse large B-cell lymphoma (DLBCL) are associated with a poor prognosis. The REMARC phase III trial (NCT01122472) showed that lenalidomide maintenance prolonged PFS in rituximab-chemotherapy responders. We conducted a REMARC ancillary study analysing the impact of lenalidomide maintenance on the prognostic value of low NKCCs. Blood samples from 335 elderly French patients enrolled in the REMARC trial were analysed by flow cytometry to obtain NKCCs at diagnosis (n = 220), at randomization (n = 186) and/or six months after randomization (n = 184). Baseline NKCCs < 100 cells/µl were associated with shorter PFS and OS (HRs = [2.2 (1.4, 3.3), p < 0.001] and [2.8 (1.7, 4.5), p < 0.001], respectively), independently of aaIPI. In a competing risk analysis, low NKCCs at baseline were associated with a higher risk of relapse/progression (p = 0.0025), but not of death without progression (p = 0.33). Lenalidomide did not affect the prognosis value of low baseline NKCCs (p  = 0.6349). Similar results were obtained for low NKCCs at randomization. Our results demonstrate that low NKCCs at baseline and post rituximab-chemotherapy are robust prognostic factors in DLBCL and reveal that lenalidomide has no impact on this parameter. Other therapeutic strategies aiming at improving NK-cell function could improve outcomes in DLBCL.

IDH2 and TET2 mutations synergize to modulate T Follicular Helper cell functional interaction with the AITL microenvironment.

Angioimmunoblastic T cell lymphoma (AITL) is a peripheral T cell lymphoma that originates from T follicular helper (Tfh) cells and exhibits a prominent tumor microenvironment (TME). IDH2 and TET2 mutations co-occur frequently in AITL, but their contribution to tumorigenesis is poorly understood. We developed an AITL mouse model that is driven by Idh2 and Tet2 mutations. Malignant Tfh cells display aberrant transcriptomic and epigenetic programs that impair TCR signaling. Neoplastic Tfh cells bearing combined Idh2 and Tet2 mutations show altered cross-talk with germinal center B cells that promotes B cell clonal expansion while decreasing Fas-FasL interaction and reducing B cell apoptosis. The plasma cell count and angiogenesis are also increased in the Idh2-mutated tumors, implying a major relationship between Idh2 mutation and the characteristic AITL TME. Our mouse model recapitulates several features of human IDH2-mutated AITL and provides a rationale for exploring therapeutic targeting of Tfh-TME cross-talk for AITL patients.

Efficacy of a short sandwich protocol, methotrexate, gemcitabine, L-asparaginase and dexamethasone chemotherapy combined with radiotherapy, in localised newly diagnosed NK/T-cell lymphoma: A French retrospective study.

Extranodal NK/T-cell lymphoma, nasal type is a rare and aggressive form of lymphoma, historically associated with poor prognosis. We report here the results of a retrospective multi-centre study evaluating the efficacy of MGAD (methotrexate, gemcitabine, L-asparaginase and dexamethasone) regimen (two cycles) combined with 'sandwich' radiotherapy in 35 patients with localised newly diagnosed extranodal NK/T-cell lymphoma. Thirty-two patients (91%) reached complete remission. With a long median follow-up of 59.6 months, progression-free and overall survival at 2 and 5 years were 71%, 80% and 53%, 73%, respectively. Around one third of the patients experienced relapse within a median time of 14.5 months. Side-effects were manageable with grades 3-4 cytopenias, mucositis and infection in 50%, 24% and 21% of the cases, respectively. Monitoring of asparaginase activity was performed in 13 patients and showed inactivation of the drug in seven (54%) patients. Our results indicate that a short therapy by sandwich MGAD chemoradiotherapy is a tolerable and effective treatment option in localised newly diagnosed extranodal NK/T-cell lymphoma patients.

Monomorphic epitheliotropic intestinal T-cell lymphoma comprises morphologic and genomic heterogeneity impacting outcome.

Monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL) is a rare aggressive T-cell lymphoma most reported in Asia. We performed a comprehensive clinical, pathological and genomic study of 71 European MEITL patients (36 males, 35 females, median age 67 years). The majority presented with gastrointestinal involvement and had emergency surgery, and 40% had stage IV disease. The tumors were morphologically classified into two groups: typical (58%) and atypical (i.e., non-monomorphic or with necrosis, angiotropism or starry-sky pattern) (42%), sharing a homogeneous immunophenotypic profile (CD3+ [98%] CD4- [94%] CD5- [97%] CD7+ [97%] CD8+ [90%] CD56+ [86%] CD103+ [80%] cytotoxic marker+ [98%]) with more frequent expression of TCRgd (50%) than TCRab (32%). MYC expression (30% of cases) partly reflecting MYC gene locus alterations, correlated with non-monomorphic cytology. Almost all cases (97%) harbored deleterious mutation(s) and/or deletion of the SETD2 gene and 90% had defective H3K36 trimethylation. Other frequently mutated genes were STAT5B (57%), JAK3 (50%), TP53 (35%), JAK1 (12.5%), BCOR and ATM (11%). Both TP53 mutations and MYC expression correlated with atypical morphology. The median overall survival (OS) of 63 patients (43/63 only received chemotherapy after initial surgery) was 7.8 months. Multivariate analysis found a strong negative impact on outcome of MYC expression, TP53 mutation, STAT5B mutation and poor performance status while aberrant B-cell marker expression (20% of cases) correlated with better survival. In conclusion, MEITL is an aggressive disease with resistance to conventional therapy, predominantly characterized by driver gene alterations deregulating histone methylation and JAK/STAT signaling and encompasses genetic and morphologic variants associated with very high clinical risk.