Cutaneous Lymphoproliferative Disorders Research Articles

Cutaneous Involvement by Refractory Celiac Disease Type 2 Histologically Mimicking Mycosis Fungoides.

Refractory celiac disease (RCD) is a rare condition characterized by persistent malabsorptive symptoms and villous atrophy despite a gluten-free diet. While RCD type 1 has a normal intraepithelial lymphocyte phenotype, RCD type 2 is defined by the presence of immunophenotypically aberrant and monoclonal intraepithelial T lymphocytes, with a high propensity to transform to enteropathy-associated T-cell lymphoma (EATL). Although dermatological manifestations of celiac disease are common, presentation with cutaneous involvement by abnormal lymphocytes of RCD type 2 or EATL is rare, with few histologic descriptions in the literature. We describe the case of a 66-year-old man with a history of celiac disease presenting with a generalized, erythematous papular rash over his torso, upper arms, and legs. Biopsy of his skin lesions showed prominent hyperkeratosis with underlying spongiosis and interface change. Increased intraepithelial (epidermotropic) lymphocytes were observed, out of proportion to the level of spongiosis, but not overly atypical in appearance. Immunohistochemistry revealed an aberrant T-cell immunophenotype (CD3/2/7 positive; CD5/4/8 negative), raising suspicion for a cutaneous T-cell lymphoproliferative disorder. A duodenal biopsy demonstrated total villous atrophy with a morphologically bland population of epitheliotropic T lymphocytes showing the same aberrant immunophenotype. Similar cells were also identified by flow cytometry in the peripheral blood. In conjunction with the history of celiac disease, a diagnosis of RCD type 2 or 'EATL in situ' with cutaneous involvement was made. Cutaneous RCD type 2 or EATL should be considered as differential diagnoses in patients with a history of celiac disease and histopathology reminiscent of epidermotropic forms of cutaneous T-cell lymphoma.

Cutaneous Post-transplant Lymphoproliferative Disorder

Cutaneous Post-transplant Lymphoproliferative Disorder

DUSP22-rearranged primary cutaneous CD30-positive T-cell lymphoproliferative disorders and adult T-cell leukemia/lymphoma frequently share the LEF1+/TIA1− immunophenotype

DUSP22 rearrangements are genetic alterations observed in a subset of systemic anaplastic large cell lymphoma (S-ALCL), primary cutaneous anaplastic large cell lymphoma (C-ALCL), and lymphomatoid papulosis (LyP). Previous investigations have shown that the LEF1+/TIA1− immunoprofile and MSC E116K mutations are highly associated with DUSP22 rearrangement in ALCL. However, the existing literature primarily focuses on S-ALCL. Our understanding of the LEF1/TIA1 immunoprofile and MSC mutation status in C-ALCL/LyP is still limited. In this study, we aimed to assess LEF1/TIA1 expression and MSC mutations in a cohort of 23 C-ALCL/LyP cases, along with a control group of histological mimickers. DUSP22 rearrangements were detected by fluorescence in situ hybridization in eight cases (6/10 C-ALCL, 2/13 LyP). We found LEF1 expression in five out of eight (63%) DUSP22-rearranged cases (3/6 C-ALCL, 2/2 LyP), and none of the 15 cases lacking DUSP22 rearrangements. Furthermore, we also found frequent LEF1 expression in adult T-cell leukemia/lymphoma (ATLL; 10 of 11, 91%) within the control group. TIA1 expression was consistently negative in all DUSP22-rearranged C-ALCL/LyP and ATLL cases tested. MCS E116K mutation was identified in one of five DUSP22-rearranged C-ALCL cases. RNA sequencing of a DUSP22-rearranged C-ALCL revealed a novel DUSP22::SNHG fusion coexisting with a CD58::WNT2B fusion. In conclusion, our findings demonstrated a lower rate of LEF1 expression in DUSP22-rearranged C-ALCL/LyP compared to previous reports that predominantly focused on S-ALCL. Moreover, we observed that the majority of ATLL cases also expressed LEF1, suggesting that the LEF1+/TIA1− immunoprofile does not differentiate DUSP22-rearranged C-ALCL/LyP from ATLL.

Primary Cutaneous Acral CD8-Positive Lymphoproliferative Disorder: A Case Report With Nonacral Presentation.

In this study, we describe a patient of primary cutaneous acral CD8-positive lymphoproliferative disorder located in a nonacral region. A 65-year-old male presented with an ill-defined lesion of rubbery consistency and a maximum diameter of 2.5 cm localized in the right thigh. Histologically, it was composed of a diffuse dermal infiltration of medium-sized atypical lymphocytes that expressed CD3, CD8, and TIA-1. In addition, a characteristic paranuclear positivity with CD68 was observed. During the follow-up, the patient had a recurrence of the disease in the abdomen with a lesion showing similar morphology and phenotype. To our knowledge, < 20 patients of primary cutaneous acral CD8-positive lymphoproliferative disorder with a nonacral presentation have been described in English literature. Although rare, its identification is essential to differentiate it from other T-cell lymphoma that express CD8 and cytotoxic markers, and whose clinical courses are very aggressive.

Paediatric onset lymphomatoid papulosis: results of a multicentre retrospective cohort study, on behalf of the EORTC Cutaneous Lymphoma Tumours Group (CLTG).

Lymphomatoid Papulosis (LyP) is a rare cutaneous T-cell lymphoproliferative disorder. Comprehensive data on LyP in the paediatric population is scarce. To characterize epidemiological, clinical, histopathological, and prognostic features of paediatric LyP. This was a retrospective, multicentre international cohort study including 87 cases of children and adolescents with LyP diagnosed between 1998 and 2022. Patients aged ≤ 18 years old at disease onset were included. Diagnosis was made in each centre based on clinical-pathological correlation. Eighty-seven patients from 12 centres were included. The mean age at onset was 7.0 years (range 3 months-18 years) with a male to female ratio of 2:1. The mean time between onset of first cutaneous lesions and diagnosis was 1.3 years (range 0-14 years). Initial misdiagnosis concerned 26.4% of patients. Initially, LyP was most often misdiagnosed as Pityriasis lichenoides et varioliformis acuta (PLEVA), insect bites, or mollusca contagiosa. Erythematous papules or papulonodules were the most frequent clinical presentation. Pruritus was specifically mentioned for 20.7% of patients. The main histological subtype was type A in 55.1% of the cases. If analysed, monoclonal TCR rearrangement was found in 76.5% of the skin biopsies. The overall survival rate was 100% with follow up at 5 years available for 33 patients and at 15 years for 8 patients. A development of associated haematological malignancy (HM) occurred in 9.6% of the cases (7/73), including four mycosis fungoides (MF) cases, one primary cutaneous anaplastic large cell lymphoma (pc-ALCL), one systemic ALCL and one case of acute myeloid leukaemia. If we compare incidence rates of cancer with the world 0-19 years old population from 2001-2010, we estimate a significantly higher risk of associated malignancy in general, occurring before the age of 19 years old with incidence rate ratio of 87.49 (CI 86.01-88.99). We report epidemiological data from a large international cohort of children and adolescents with LyP. Overall the prognosis of the disease is good, with excellent survival rates for all patients. Due to increased risk of associated HM, a long-term follow-up should be recommended for LyP patients.

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

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

Exploring cutaneous lymphoproliferative disorders in the wake of COVID‐19 vaccination

AbstractBackgroundIndividual reports have described lymphoproliferative disorders (LPDs) and cutaneous lymphomas emerging after administration of the COVID‐19 vaccine; however, the relationship between reactions and vaccine types has not yet been examined.ObjectiveDetermine if there are cases of cutaneous LPDs associated with certain COVID‐19 vaccines and their outcomes.MethodsWe analysed PubMed, the Vaccine Adverse Events Reporting System (VAERS), and our database for instances of biopsy‐proven LPDs following COVID‐19 vaccines.ResultsFifty cases of biopsy‐proven LPDs arising after COVID‐19 vaccination were found: 37 from medical literature, 11 from VAERS and two from our institution. Geographical distribution revealed the most cases in the United States, Italy, and Greece, with single cases in Spain, Colombia, Canada, Japan, and Romania. The average age of patients was 53; with a slight male predominance (male‐to‐female ratio of 1.5:1). The Pfizer‐BioNTech vaccine was associated with LPDs in 36/50 (72%) cases, aligning with its 70% share of the global vaccine market. Histopathology revealed CD30+ in 80% of cases. The most prevalent form of LPD was lymphomatoid papulosis (LyP, 30%). All reported cases produced favourable outcomes (either complete or near‐complete remission). Therapeutic approaches ranged from observation to treatment with steroids, methotrexate, or excision.ConclusionLPDs after COVID‐19 vaccination appear in the context of the same vaccines (proportionally to their global market shares), share clinical and pathological findings, and have indolent, self‐limited character.

Cutaneous lymphoproliferative disorders: Back to the future.

In the 1980s, immunohistochemistry and clonality analyses became instrumental in the recognition and definition of new types of cutaneous T-cell lymphoma (CTCL) and cutaneous B-cell lymphoma (CBCL) and the development of new classifications. By accepting loss of pan-T-cell antigens and clonal T-cell receptor gene rearrangements as important criteria to differentiate between benign and malignant T-cell proliferations, and monotypic immunoglobulin light-chain expression and clonal immunoglobulin gene rearrangements as crucial criteria to distinguish between benign and malignant B-cell proliferations, many cases, until then diagnosed as cutaneous lymphoid hyperplasia or pseudolymphoma, were reclassified as primary cutaneous CD4+ small/medium T-cell lymphoma (PCSM-TCL) or primary cutaneous marginal zone lymphoma (PCMZL), respectively. However, in recent years there is growing awareness that neither these immunohistochemical criteria nor demonstration of T-cell or B-cell clonality is specific for malignant lymphomas. In addition, many studies have reported that these low-grade malignant CTCL and CBCL have an indolent clinical behavior and an excellent prognosis with disease-specific survival rates of or close to 100%. As a result, recent classifications have downgraded several low-grade malignant cutaneous lymphomas to lymphoproliferative disorder (LPD). Both the 5th edition of the WHO classification (2022) and the 2022 International Consensus Classification (ICC) of mature lymphoid neoplasms reclassified PCSM-TCL as primary cutaneous CD4+ small/medium T-cell LPD and primary cutaneous acral CD8+ T-cell lymphoma as primary cutaneous acral CD8+ T cell LPD. While the 2022 ICC introduced the term "primary cutaneous marginal zone LPD," in the 5th edition of the WHO classification PCMZL is maintained. In this review we describe the background and rationale of the continually changing terminology of these conditions and discuss the clinical consequences of downgrading malignant lymphomas to LPDs.

Primary Cutaneous CD4 Small/Medium T-Cell Lymphoproliferative Disorder Following COVID-19 Vaccination-What Do We Know about Lymphoproliferative Disorders and Cutaneous Lymphomas after COVID-19 Vaccination? A Report of an Atypical Case and a Review of the Literature.

The association between Primary cutaneous CD4 small/medium T-cell lymphoproliferative disorder (PCSM-TCLPD) and COVID-19 immunization has been sparsely documented in the medical literature. Reviewing the literature, albeit infrequently, we can find cases of the recurrence and new onset of lymphoproliferative processes and cutaneous lymphomas following the COVID-19 vaccine. Many of the entities we encounter are classified as cutaneous lymphoproliferative disorders. The prevailing hypothesis suggests that the predominant cutaneous reactions to SARS-CoV-2 vaccines may stem from T-cell-mediated immune activation responses to vaccine components, notably messenger RNA (mRNA). Specifically, it is posited that the presence of cutaneous lymphoid infiltrates may be linked to immune system stimulation, supported by the absence, to date, of instances of primary cutaneous B-cell lymphoma following mRNA vaccination. Within this context, it is imperative to underscore that the etiological association between PCSM-TCLPD and COVID-19 vaccination should not discourage vaccination efforts. Instead, it underscores the necessity for continuous surveillance, in-depth investigation, and comprehensive follow-up studies to delineate the specific attributes and underlying mechanisms of such cutaneous manifestations post vaccination.

Primary Cutaneous CD30-Positive Lymphoproliferative Disorders—Current Therapeutic Approaches with a Focus on Brentuximab Vedotin

One of the most common subgroups of cutaneous T-cell lymphomas is that of primary cutaneous CD30-positive lymphoproliferative disorders. The group includes lymphomatoid papulosis (LyP) and primary cutaneous anaplastic large cell lymphoma (pcALCL), as well as some borderline cases. Recently, significant progress has been made in understanding the genetics and treatment of these disorders. This review article summarises the clinical evidence supporting the current treatment options for these diseases. Recent years have seen the introduction of novel agents into clinical practice; most of these target CD30, such as anti-CD30 monoclonal antibodies and conjugated antibodies (brentuximab vedotin), bispecific antibodies and cellular therapies, particularly anti-CD30 CAR-T cells. This paper briefly reviews the biology of CD30 that makes it a good therapeutic target and describes the anti-CD30 therapies that have emerged to date.

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

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

Cutaneous lymphoproliferative disorders after COVID-19 vaccination: clinical presentation, histopathology, and outcomes

Individual reports described lymphoproliferative disorders (LPDs) after COVID-19 vaccination; however, the relationship between cases is unexamined. We aim to determine if there are cases of cutaneous LPDs associated with COVID-19 vaccination and their outcomes. We present a review of world literature, vaccine registries, and two unreported cases of LPDs after COVID-19 vaccination. Review of the medical literature, VAERS, and our two cases reveal predominance of Pfizer-BioNTech vaccine, younger patients, and males. All cases resulted in favorable outcomes. Approximately 84% of cases demonstrated CD30+ positivity in their skin biopsies, suggesting that an antigenic trigger may lead to a type IV adaptive immune response, with clonal expansion of CD30+ T-cells and subsequent oncogenic mutational hits eventuating in transient LPDs. LPDs after COVID-19 vaccination appear in the context of the same vaccines (proportionally to their global market shares), share clinical and pathological findings, and have indolent, self-limited character.

Primary cutaneous acral CD8-positive T-cell lymphoproliferative disorder: A clinical and histologic retrospective cohort study

Clonally restricted, non-epidermotropic, low-grade, CD8-positive T-cell infiltrates of the skin was recognized as a unique form of indolent CD8-positive lymphoproliferative disease in 2007 when it was first called primary cutaneous indolent CD8-positive lymphoid proliferation. More recently, the designation of primary cutaneous acral CD8-positive T-cell lymphoproliferative disorder has been used. It is unique as a cutaneous lymphoproliferative disorder because of relative uniformity in its clinical presentation and histomorphology. It has been recognized as having an interesting predilection for the ear and acral sites, characteristically presenting as a solitary lesion. The basic morphology is one characterized by a non-epidermotropic, tumefactive infiltrate of well-differentiated, noncerebriform, atypical, small- to intermediate-sized lymphocytes that exhibit a specific phenotype characterized by CD8 and TIA positivity in concert with a distinct perinuclear Golgi staining pattern for CD68. The typical presentation is in the context of a solitary lesion, which can be treated surgically or with local irradiation. We describe in detail two very unusual cases that expand the clinical spectrum of this condition given the non-acral localization, the multiplicity of lesions to involve the trunk and extremities, and, in one case, the stable but recalcitrant course over 30 years. In addition, the second patient developed paraneoplastic dermatomyositis. We also retrospectively review our database for other cases that represent the entity of primary cutaneous acral CD8-positive T-cell lymphoproliferative disorder and review the literature focusing on non-acral cases. Nomenclature evolution from its first recognition in 2007 to the present is discussed.

BI19 Cutaneous post-transplant lymphoproliferative disorder in an immunosuppressed patient

Abstract Post-transplant lymphoproliferative disorders (PTLDs) are a common form of de novo neoplasia developing in patients with immunosuppression following a transplant. The majority are associated with Epstein–Barr virus (EBV) infection. Cutaneous PTLD manifestations are rare and not well documented in literature. We present a case of systemic PTLD with secondary extensive cutaneous involvement 4 months after allogenic stem cell transplant for JAK2-mutated myelofibrosis. A 68-year-old man was admitted to the haematology department with fevers, diarrhoea, cytopenia, EBV viraemia and a nodular rash behind his ears. Biopsies from colonoscopy confirmed monomorphic PTLD with subsequent extensive ileocalceal lymphadenopathy area detected on computed tomography. Asymptomatic, large, hardened violaceous nodules on the head and neck worsened further. Skin biopsy showed an infiltrate of atypical lymphocytes in the dermis, composed predominantly of large lymphoid cells with visible prominent nucleoli. A limited immunohistochemical panel showed positivity for BCL-2 but not CD20. EBV-encoded RNA in situ hybridization was also positive. Features were compatible with cutaneous involvement by the known monomorphic PTLD. Unfortunately, the patient deteriorated with haemodynamic instability due to sepsis, despite two further infusions of rituximab, and was directed to the palliative team. He died soon after the discontinuation of all treatments. PTLD has a wide spectrum of clinical manifestations. It is classified into three nondestructive types: polymorphic, monomorphic and classic Hodgkin lymphoma type. It can have a poor prognosis so it should always be considered as a diagnosis in transplant patients. Monomorphic PTLDs tend to be more aggressive and rarely respond to immunosuppression reduction. On the contrary, primary cutaneous involvement is rare and seems to have a favourable outcome. Treatment depends on the severity of the disease, and both localized and systemic therapies have been used. Transplant patients should have long-term follow-up to diagnose and promptly treat possible complications.

What is new about primary cutaneous B cell lymphomas.

Primary cutaneous B-cell lymphomas (CBCL) are a heterogeneous group of B-cell lymphomas without evidence of extracutaneous disease at the time of diagnosis. The 2022 World Health Organization classification of mature lymphoid neoplasms differentiates the indolent primary cutaneous marginal zone lymphoproliferative disorder, primary cutaneous follicle center lymphoma and Epstein-Barr virus-positive mucocutaneous ulcer, from the more aggressive primary cutaneous diffuse large B-cell lymphoma, leg-type and intravascular large B-cell lymphoma. The new updates in the 2022 classification are based on recent scientific advances in the understanding and characterization of these entities. This article aims to review the main clinical, cellular and molecular features of the five CBCL subsets along with their management and treatment. The exponentially growing evidence for new treatment options for systemic B-cell lymphomas raises expectations for the field of CBCL as well. However, specific prospective high quality research on CBCL is still crucial to further define their management and update international guidelines.

Primary Cutaneous Marginal Zone Lymphoproliferative Disorder of Donor Origin after Allogeneic Hematopoietic Stem Cell Transplantation.

Primary cutaneous posttransplant lymphoproliferative disorders (PTLDs) after allogeneic hematopoietic stem cell transplant (allo-HSCT) are exceedingly rare, with only 6 published cases, all of them consisting in T-cell neoplasms. In this report, we present for the first time a donor-derived B-cell PTLD consisting in a primary, cutaneous, B-cell, marginal zone, lymphoproliferative disorder (PCMZLPD). The patient, a 37-year-old woman with a history of Hodgkin lymphoma received an allo-HSCT from her healthy, matched, related father, achieving complete host chimerism in the bone marrow and peripheral blood. However, 8 years after the allo-HSCT, she presented asymptomatic skin lesions consisting in oval, well-defined, slightly raised erythematous plaques, located on the arms, trunk, and legs. Skin biopsies of 2 lesions demonstrated a class-switched IgG+, EBV-, PCMZLPD, showing kappa light chain restriction and monoclonal rearrangement of the IgH gene. Microsatellite genotyping and 2-color fluorescence in situ hybridization (X and Y chromosomes) confirmed that the origin of the neoplastic cells was the donor graft. The lesions showed an indolent behavior, good response to topical corticosteroids, and no need for systemic treatment. Our case broadens the spectrum of PTLD, a diverse group of lymphoid and/or plasmacytic proliferations with variable clinical presentations and histopathological features.

Transdifferentiation, phenotypic infidelity, progression, and transformation in T/NK-cell neoplasms: Report from the 2021 SH/EAHP Workshop.

Sessions 8 and 9 of the 2021 Society for Hematopathology and the European Association for Haematopathology Workshop aimed to collect examples of transdifferentiation, lineage infidelity, progression, and transformation in precursor and mature T/natural killer (NK)-cell neoplasms. Twenty-eight cases were submitted and analyzed, with whole-exome sequencing and genome-wide RNA expression analysis performed in a subset of the cases. In session 8, 7 T-lymphoblastic lymphoma/leukemia cases were received that showed transdifferentiation to clonally related mature myeloid hematopoietic neoplasms, including 6 histiocytic/dendritic cell lineage neoplasms and a mast cell sarcoma. Session 9 included 21 mature T-cell neoplasms that were grouped into 3 themes. The first one addressed phenotypic infidelity in mature T-cell lymphomas (TCLs) and included 8 TCLs expressing aberrant antigens, mimicking classic Hodgkin and non-Hodgkin B-cell lymphomas. The second theme addressed disease progression in TCL and included 5 cutaneous T-cell lymphoproliferative disorders and 2 T-cell large granular lymphocyte proliferations with subsequent progression to systemic TCL. The third theme included 6 patients with TCL with T-follicular helper phenotype, mainly angioimmunoblastic T-cell lymphoma, with concurrent/subsequent clonal hematopoiesis or myeloid neoplasms and/or subsequent/concomitant diffuse large B-cell lymphoma. This cohort of cases allowed us to illustrate, discuss, and review current concepts of transdifferentiation, aberrant antigen expression, and progression in various T/NK-cell neoplasms.

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.

269 Mucosal CD30-positive T-cell lymphoproliferations arising in the patient with cutaneous CD30-positive T-cell lymphoproliferative disorders

269 Mucosal CD30-positive T-cell lymphoproliferations arising in the patient with cutaneous CD30-positive T-cell lymphoproliferative disorders

The Distinctive Nature of Thyroid MALT Lymphomas Including IRTA1 Expression.

Mucosa-associated lymphoid tissue (MALT) lymphomas often express IgM and IRTA1 with only a minority demonstrating plasmacytic differentiation. However, like primary cutaneous marginal zone lymphoproliferative disorders (PCMZLPD), thyroid MALT lymphomas (T-MALT-L) frequently show plasmacytic differentiation and IgG positivity. Whether T-MALT-L share other features with PCMZLPD, including frequent IgG4 positivity and infrequent IRTA1 expression, and how IRTA1 staining compares to that in Hashimoto thyroiditis (HT) are unknown. Therefore, the clinicopathologic features of 18 T-MALT-L were assessed, and their IRTA1 expression compared with that in 5 HT cases. All T-MALT-L cases included a B-lymphoid component. Plasmacytic differentiation was present in 15 cases and was extensive in 12. Fourteen cases were IgG+ including 2 IgG4+ (12 κ+, 2 κ-/λ-). One case was IgAλ+. Plasmacytic cells were uniformly CD19+/CD56- but CD138- in 7/15 cases. IRTA1+ cells were present in 16/16 cases, ranging from scattered cells to >50%. They were often concentrated in "MALT ball"-type lymphoepithelial lesions, perifollicular regions, and sometimes in germinal centers. IRTA1 positivity was also present in all HT cases, although it was never very extensive and often had a perifollicular distribution, occasionally with sparse aggregates and positive cells within rare thyroid follicles. Thus, T-MALT-L share some features with PCMZLPD but are more similar to noncutaneous MALT lymphomas, with prominent lymphoepithelial lesions, ubiquitous although variable IRTA1 positivity, and infrequent IgG4 positivity. Plasmacytic differentiation is also common although CD138 loss is frequent and light chain staining may be absent. IRTA1 staining may help in the differential diagnosis with HT, although there is some overlap in staining patterns.