Expression of TFH Markers and Detection of RHOA p.G17V and IDH2 p.R172K/S Mutations in Cutaneous Localizations of Angioimmunoblastic T-Cell Lymphomas

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.

Deciphering the spectrum of cutaneous lymphomas expressing TFH markers

T-follicular helper (TFH) markers are expressed in the microenvironnement of marginal zone B-cell lymphoma (MZL), and in lymphomas arising from TFH-cells, sometimes making the differential diagnosis difficult. In the skin, the "TFH-spectrum" is poorly defined, going from primary cutaneous lymphoproliferative disorder with small/medium CD4+ T-cells (SMLPD) to cutaneous localizations of systemic angioimmunoblastic T-cell lymphoma (cAITL), and may pass through intermediate forms (primary cutaneous T-follicular helper derived lymphoma, not otherwise specified (PCTFHL,NOS)). We retrospectively analyzed 20 MZL, 13 SMLPD, 5 PCTFHL, and 11 cAITL clinically, histologically, and molecularly, to define tools to differentiate them. Characteristics that might favor the diagnosis of MZL over SMLPD are: multiple skin nodules (p < 0.001), nodular architecture (p < 0.01), residual germinal centers with follicular dendritic cell network (p < 0.001), monotypic plasma cells (p < 0.001), and few staining with PD1 (p = 0.016) or CXCL13 (p = 0.03). PCTFHL and cAITL presented as multiple (p < 0.01) lesions, in older patients (p < 0.01), with systemic symptoms and/or biological alterations (p < 0.01). Immunophenotypic loss of T-cell markers (p < 0.001), BCL6 (p = 0.023) and/or CD10 staining (p = 0.08), and a higher proliferative index (≥ 30%, p = 0.039) favoured these diagnoses over SMLPD. Pathogenic variants were observed by genomic sequencing in 47% of MZL (TNFAIP3 (32%), EP300 (21%), NOTCH2 (16%), KMT2D (16%), CARD11 (10.5%)), 8% of SMLPD (TET2), 40% of PCTFHL (SOCS1 (20%), ARID1A (20%)) and 64% of cAITL (TET2 (63.6%), RHOA (36.4%), NOTCH1 (9%)). This study characterizes the various clinical and histological features between cutaneous lymphomas expressing TFH markers and highlights the value of the interest of screening for genomic mutations in difficult cases.

Epigenetic regulation in hematopoiesis and its implications in the targeted therapy of hematologic malignancies

Hematologic malignancies are one of the most common cancers, and the incidence has been rising in recent decades. The clinical and molecular features of hematologic malignancies are highly heterogenous, and some hematologic malignancies are incurable, challenging the treatment, and prognosis of the patients. However, hematopoiesis and oncogenesis of hematologic malignancies are profoundly affected by epigenetic regulation. Studies have found that methylation-related mutations, abnormal methylation profiles of DNA, and abnormal histone deacetylase expression are recurrent in leukemia and lymphoma. Furthermore, the hypomethylating agents and histone deacetylase inhibitors are effective to treat acute myeloid leukemia and T-cell lymphomas, indicating that epigenetic regulation is indispensable to hematologic oncogenesis. Epigenetic regulation mainly includes DNA modifications, histone modifications, and noncoding RNA-mediated targeting, and regulates various DNA-based processes. This review presents the role of writers, readers, and erasers of DNA methylation and histone methylation, and acetylation in hematologic malignancies. In addition, this review provides the influence of microRNAs and long noncoding RNAs on hematologic malignancies. Furthermore, the implication of epigenetic regulation in targeted treatment is discussed. This review comprehensively presents the change and function of each epigenetic regulator in normal and oncogenic hematopoiesis and provides innovative epigenetic-targeted treatment in clinical practice.

Primary cutaneous peripheral T-cell lymphomas with a T-follicular helper phenotype: an integrative clinical, pathological and molecular case series study

BACKGROUND

Primary cutaneous peripheral T-cell lymphomas with a T-follicular helper phenotype (pcTFH-PTCL) are poorly characterized, and often compared to, but not corresponding with, mycosis fungoides (MF), Sézary syndrome, primary cutaneous CD4⁺ lymphoproliferative disorder, and skin manifestations of angioimmunoblastic T-cell lymphomas (AITL).

OBJECTIVES

We describe the clinicopathological features of pcTFH-PTCL in this original series of 23 patients, and also characterize these cases molecularly.

METHODS

Clinical and histopathological data of the selected patients were reviewed. Patient biopsy samples were also analysed by targeted next-generation sequencing.

RESULTS

All patients (15 men, eight women; median age 66 years) presented with skin lesions, without systemic disease. Most were stage T3b, with nodular (n = 16), papular (n = 6) or plaque (atypical for MF, n = 1) lesions. Three (13%) developed systemic disease and died of lymphoma. Nine (39%) patients received more than one line of chemotherapy. Histologically, the lymphomas were CD4⁺ T-cell proliferations, usually dense and located in the deep dermis (n = 14, 61%), with the expression of at least two TFH markers (CD10, CXCL13, PD1, ICOS, BCL6), including three markers in 16 cases (70%). They were associated with a variable proportion of B cells. Eight patients were diagnosed with an associated B-cell lymphoproliferative disorder (LPD) on biopsy, including Epstein-Barr virus (EBV)-positive diffuse large B-cell lymphoma (n = 3), EBV⁺ LPD (n = 1) and monotypic plasma cell LPD (n = 4). Targeted sequencing showed four patients to have a mutated TET2-RHOAG17V association (as frequently seen in AITL) and another a TET2/DNMT3A/PLCG1/SETD2 mutational profile. The latter patient, one with a TET2-RHOA association, and one with no detected mutations, developed systemic disease and died. Five other patients showed isolated mutations in TET2 (n = 1), PLCG1 (n = 2), SETD2 (n = 1) or STAT5B (n = 1).

CONCLUSIONS

Patients with pcTFH-PTCL have pathological and genetic features that overlap with those of systemic lymphoma of TFH derivation. Clinically, most remained confined to the skin, with only three patients showing systemic spread and death. Whether pcTFH-PTCL should be integrated as a new subgroup of TFH lymphomas in future classifications is still a matter of debate. What is already known about this topic? There is a group of cutaneous lymphomas that express T-follicular helper (TFH) markers that do not appear to correspond to existing World Health Organization diagnostic entities. These include mycosis fungoides, Sézary syndrome, or primary cutaneous CD4⁺ small/medium-sized T-cell lymphoproliferative disorder or cutaneous extensions of systemic peripheral T-cell lymphomas (PTCL) with TFH phenotype. What does this study add? This is the first large original series of patients with a diagnosis of primary cutaneous PTCL with a TFH phenotype (pcTFH-PTCL) to be molecularly characterized. pcTFH-PTCL may be a standalone group of cutaneous lymphomas with clinicopathological and molecular characteristics that overlap with those of systemic TFH lymphomas, such as angioimmunoblastic T-cell lymphoma, and does not belong to known diagnostic groups of cutaneous lymphoma. This has an impact on the treatment and follow-up of patients; the clinical behaviour needs to be better clarified in further studies to tailor patient management.

A High Programmed Cell Death Protein 1 Hormone Receptor Score on Skin Biopsy is Associated with Sézary Syndrome Diagnosis: A Study of 91 Patients with Erythroderma

Erythroderma is challenging to diagnose. The aim of this single-centre retrospective study was to identify factors that can be used to improve the diagnosis of erythroderma. Among 91 patients with erythroderma, 21 were diagnosed with eczema, 17 with psoriasis, 20 with drug-induced erythroderma, 13 with erythrodermic mycosis fungoides and 20 with Sézary syndrome. Nail alterations, ear involvement, and severe scaling were significantly associated with psoriasis (p = 0.044). Fever and hypereosinophilia were associated with drug-induced erythroderma. Expression of programmed cell death protein 1 was observed in all skin biopsies. However, with Sézary syndrome, programmed cell death protein 1 expression was significantly higher than with other aetiologies. A programmed cell death protein 1 hormone receptor score (H-score) >50 was associated with Sézary syndrome (p < 0.001, sensitivity 75%, specificity 92%) as well as CXCL13 expression (p < 0.044). CD7 loss was more frequent with erythrodermic mycosis fungoides and Sézary syndrome (p = 0.022). This study reports the importance of programmed cell death protein 1 expression for the differential diagnosis of Sézary syndrome and other aetiologies, including erythrodermic mycosis fungoides.

Cutaneous Involvement of Angioimmunoblastic T-Cell Lymphoma Masquerading as B-Cell Reactive Lymphoid Hyperplasia

ABSTRACT

A 59-year-old woman presented with a persistent eruption manifested as multiple agminated miliary facial papules. Histopathological examination showed prominent nodular dermal lymphoid infiltrates with hyperplastic follicles that were initially interpreted as B-cell reactive lymphoid hyperplasia. Several years later, an additional biopsy showed a dense perifollicular infiltrate with reactive primary and secondary follicles. Accompanying T cells corresponded to CD3/CD4/PD1/CXCL13-positive cells and scattered Epstein-Barr virus-positive B cells were identified by in situ hybridization. A monoclonal T-cell population was demonstrated by TCRγ and TCRβ Polymerase Chain Reaction amplification, as well as a minor abnormal circulating T-cell population by flow cytometry (0.62% of the white blood cells, CD4+CD3s-CD7-). A biopsy specimen from an enlarged right supraclavicular lymph node disclosed nodal involvement by angioimmunoblastic T-cell lymphoma. The observation of B-cell dermal nodular infiltrates with well-demarcated lymphoid aggregates forming primary lymphoid follicles may lead to overlook the T-cell component in some cases of angioimmunoblastic T-cell lymphoma. In such cases, a careful assessment of the apparently minor T-cell component is important to establish a correct diagnosis.

Hodgkin Reed-Sternberg-Like Cells in Non-Hodgkin Lymphoma

Reed-Sternberg cells (RSCs) are hallmarks of classic Hodgkin lymphoma (cHL). However, cells with a similar morphology and immunophenotype, so-called Reed-Sternberg-like cells (RSLCs), are occasionally seen in both B cell and T cell non-Hodgkin Lymphomas (NHLs). In NHLs, RSLCs are usually present as scattered elements or in small clusters, and the typical background microenviroment of cHL is usually absent. Nevertheless, in NHLs, the phenotype of RSLCs is very similar to typical RSCs, staining positive for CD30 and EBV, and often for B cell lineage markers, and negative for CD45/LCA. Due to different therapeutic approaches and prognostication, it is mandatory to distinguish between cHL and NHLs. Herein, NHL types in which RSLCs can be detected along with clinicopathological correlation are described. Moreover, the main helpful clues in the differential diagnosis with cHL are summarized.

Primary Cutaneous CD4+ Small/Medium T-Cell Lymphoproliferative Disorders: A Clinical, Pathologic, and Molecular Study of 60 Cases Presenting With a Single Lesion: A Multicenter Study of the French Cutaneous Lymphoma Study Group

Primary cutaneous CD4 small/medium T-cell lymphoproliferative disorder (PCSMLPD) is a recently recognized entity in the 2017 World Health Organization (WHO) classification. It belongs to the T-follicular helper (TFH) lymphoproliferations. The clinical, pathologic, and molecular features of this localized disease are underresearched. We conducted a retrospective multicentric study of 60 patients with a PCSMLPD that presented as a single cutaneous lesion. Clinical, pathologic, and targeted molecular analyses were performed. PCSMLPD presented mostly as a nodule (45%), located on the head and neck area (50%) in adults (mean age: 59 y [43.3 to 75.2]). All patients had an indolent disease course, either at initial staging or during follow-up (mean: 16.6 mo [1.3 to 31.9]). Spontaneous regression was reported in 31.9% of cases. The infiltrates were most often nodular and/or diffuse, expanding in the whole dermis (78%, Pattern 1), rather than subepidermal band-like in the superficial dermis (22%, Pattern 2). Epidermotropism, folliculotropism, and capillary hyperplasia were common. The expression of TFH lineage markers was more extensive in lesions with Pattern 2, but a substantial B-cell infiltrate was seen in both types of lesions. A clonal rearrangement of the TCR genes was identified in 68% of cases. One sample of the 13 tested revealed a mutation in the DNMT3A gene among the 9 genes studied (TET2, DNMT3A, IDH2, RHOA, SETD2, PLCG1, STAT3, STAT5B, and CD28). PCSMLPD follows a benign clinical course and can spontaneously regress after biopsy. Although PCSMLPD expresses TFH lineage markers, mutations usually found in angioimmunoblastic T-cell lymphomas are uncommon.

An Update on Molecular Biology of Cutaneous T Cell Lymphoma

Cutaneous T cell lymphomas represent a heterogenous group of lymphoproliferative disorders defined by clonal proliferation of T cells present in the skin. The latest WHO classification in 2016 and WHO-EORTC classification in 2018 has updated the classification of these entities based on the molecular profile. Research in the field of molecular genetics of CTCL has allowed a better understanding of the biology of these tumors and has helped to identify potential targets for therapy that can be tailored to individual patients. In this review, we discuss the latest developments in the molecular profile of CTCLs including biomarkers for diagnosis, prognosis, and potential therapeutic targets. We have also touched upon the utility of various molecular diagnostic modalities. For the purpose of this review, we researched papers in PubMed indexed journals in English literature published in the past 20 years using keywords CTCL, mycosis fungoides, molecular profile, molecular diagnosis, whole genome profile, genomic landscape, TCR clonality.

Defining signatures of peripheral T-cell lymphoma with a targeted 20-marker gene expression profiling assay

Peripheral T-cell lymphoma comprises a heterogeneous group of mature non-Hodgkin lymphomas. Their diagnosis is challenging, with up to 30% of cases remaining unclassifiable and referred to as “not otherwise specified”. We developed a reverse transcriptase-multiplex ligation-dependent probe amplification gene expression profiling assay to differentiate the main T-cell lymphoma entities and to study the heterogeneity of the “not specified” category. The test evaluates the expression of 20 genes, including 17 markers relevant to T-cell immunology and lymphoma biopathology, one Epstein-Barr virus-related transcript, and variants of RHOA (G17V) and IDH2 (R172K/T). By unsupervised hierarchical clustering, our assay accurately identified 21 of 21 ALK-positive anaplastic large cell lymphomas, 16 of 16 extranodal natural killer (NK)/T-cell lymphomas, 6 of 6 hepatosplenic T-cell lymphomas, and 13 of 13 adult T-cell leukemia/lymphomas. ALK-negative anaplastic lymphomas (n=34) segregated into one cytotoxic cluster (n=10) and one non-cytotoxic cluster expressing Th2 markers (n=24) and enriched in DUSP22-rearranged cases. The 63 T_FH-derived lymphomas divided into two subgroups according to a predominant T_FH (n=50) or an enrichment in Th2 (n=13) signatures. We next developed a support vector machine predictor which attributed a molecular class to 27 of 77 not specified T-cell lymphomas: 17 T_FH, five cytotoxic ALK-negative anaplastic and five NK/T-cell lymphomas. Among the remaining cases, we identified two cell-of-origin subgroups corresponding to cytotoxic/Th1 (n=19) and Th2 (n=24) signatures. A reproducibility test on 40 cases yielded a 90% concordance between three independent laboratories. This study demonstrates the applicability of a simple gene expression assay for the classification of peripheral T-cell lymphomas. Its applicability to routinely-fixed samples makes it an attractive adjunct in diagnostic practice.

Cutaneous lesions of angioimmunoblastic T-cell lymphoma: Clinical, pathological, and immunophenotypic features

BACKGROUND

Angioimmunoblastic T-cell lymphoma (AITL) is a systemic peripheral T-cell lymphoma with a follicular helper T-cell (T_FH ) immunophenotype that frequently involves the skin. However, the histopathology of cutaneous involvement by AITL has not been fully established.

METHODS

We reviewed the clinicopathological features of 19 patients seen at our institution with AITL involving the skin. Pan-T-cell and T_FH marker expression was evaluated by immunohistochemistry. Epstein-Barr virus (EBV) was detected using in situ hybridization (ISH) for Epstein-Barr virus-encoded small RNA (EBER). T-cell receptor (TCR) gene rearrangement was evaluated by PCR.

RESULTS

AITL affected both trunk and extremities in 15/19 cases (79%). Perivascular infiltration by small and/or medium-sized lymphocytes was seen in 18/19 (95%). Granulomatous inflammation was identified in 4/19 (21%). Aberrant loss of CD2, CD5, or CD7 was identified in 1/18 (6%), 2/18 (11%), or 7/19 (37%) cases, respectively. Seventeen of eighteen evaluable cases (95%) expressed 2 to 3 T_FH markers: PD-1 in 19/19 (100%), BCL6 in 94% (17/18), and CD10 in 37% (7/19). EBV-positive cells were detected in 3/18 (17%) with varying density. Clonal TCR gene rearrangement was identified in 9/11 (82%).

CONCLUSIONS

Cutaneous involvement by AITL shows relatively non-specific histopathological features. However, an immunohistochemical panel including T_FH markers and EBER ISH is useful in differential diagnosis.

Cutaneous localization of angioimmunoblastic T-cell lymphoma may masquerade as B-cell lymphoma or classical Hodgkin lymphoma: A histologic diagnostic pitfall

BACKGROUND

We report the cases of three patients presenting skin lesions whose biopsies showed nodular polymorphic infiltrates consisting of lymphocytes, plasma cells, histiocytes, eosinophils, B blasts, and Hodgkin Reed-Sternberg (HRS)-like cells. Two of them were initially diagnosed as classical Hodgkin lymphoma (cHL), on the other hand, the last one as a B-cell lymphoma. All patients have been treated for angioimmunoblastic T-cell lymphoma (AITL).

METHODS

We performed a second review of the skin biopsies with further immunophenotypic molecular analyses. Scrupulous observation revealed, in the background of the three cases, atypical small to medium-sized lymphocytes carrying a CD3+, CD4+ T-cell phenotype and expressing PD1 and CXCL13 follicular helper T-cell markers. The two lesions initially diagnosed as cHL showed scattered HRS-like cells with CD30+, CD15+, PAX5+, CD20-, Epstein Barr Virus (EBV) + classical phenotype. The case initially diagnosed as B-cell lymphoma showed a diffuse B-cell proliferation associated with small B-cell and medium to large-sized B blasts that were positive for EBV.

CONCLUSION

Those cases highlighted that atypical T-cells may be obscured by B-cell proliferation mimicking cHL or B-cell lymphoma in cutaneous localization of AITL and confirmed the requirement of collecting clinical information before performing a diagnosis.

[Histopathology of cutaneous drug reactions]

There are many different types of cutaneous adverse reactions. The most classical reactions are driven by T lymphocytes that specifically react towards a drug, with an individual genetic susceptibility linked to certain type I major histocompatibility complex alleles. These reactions are characterized by a wide variety of clinical and histopathological presentations, and a wide range of severity. The most frequent entity is the maculopapular rash, while the most aggressive forms are the Steven-Johnson syndrome and toxic epidermal necrolysis (SJS-TEN). The histopathological alterations associated to each of these syndromes have been better described in the literature during the past 10 years, encompassing non-specific lesions, as in most drug induced maculopapular rashes, to more specific inflammatory patterns. The finding of confluent apoptotic keratinocytes with epidermal detachment is the prototypical aspect of SJS-TEN. There are however numerous pitfalls, and a similar aspect to those observed in each cutaneous drug reactions entities can be found in other diseases. DRESS syndrome can indeed present with dense and epidermotropic T-cell infiltrate, sometimes with nuclear atypias, and thus can be difficult to distinguish from a primary or secondary cutaneous T-cell lymphoma. The diagnosis of cutaneous adverse reactions relies on a clinical-pathological confrontation and requires an accurate evaluation of drug imputability.