ALK-positive anaplastic large cell lymphoma limited to the skin: clinical, histopathological and molecular analysis of 6 pediatric cases. A report from the ALCL99 study

Primary cutaneous, epidermotropic mycosis fungoides-like presentation: critical appraisal and description of two novel cases, broadening the spectrum of ALK+ T-cell lymphoma

Leading from a two-case series, including two patients receiving a diagnosis of epidermotropic T-cell lymphoma, featuring a mycosis fungoides (MF)-like clinical pattern and ALK expression and molecular alteration, we performed a critical appraisal of ALK+ primary cutaneous T-cell lymphomas (pcTCL). Considering our patients and the literature, 32 cases were retrieved, 7 of which featured an MF-like clinical picture over a 4-to-20-year period. MF-like cases show distinctive histology, comprising a predominantly epidermotropic infiltration of small-to-large, atypical-to-pleomorphic, with few anaplastic cells, negligible-to-intense CD30-expression, and a CD4+/cytotoxic granule+ phenotype. These features should prompt a search for ALK expression captured by the ALK D5F3 clone. Bona fide ALK+ pcTCL is very rare, and existent data suggest the presence of a broader pattern of disease, including instances mimicking MF and/or primary cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma. The major challenges in dealing with this subset include prodromal phases, misinterpreted as inflammatory dermatosis or parapsoriasis/early phase MF both clinically and histologically, while recognition of its ALK-driven biology is hampered both by the unusual clinic-pathologic pattern of the disease, which stands apart from the classical (i.e., nodal) picture of ALK+ anaplastic large cell lymphoma and by the low sensitivity of ALK1 clone. Data on its optimal management are far from being conclusive: An MF-like approach is currently chosen, but depending on CD30 and, most notably, ALK expression, a targeted therapy could be envisaged in advanced stages, as clinical response to ALK inhibition was documented in one patient.

Challenges in utilizing ALK expression to distinguish primary cutaneous from systemic anaplastic large cell lymphoma

Anaplastic large cell lymphoma (ALCL) is a CD30+ peripheral T-cell lymphoma with a clinical spectrum including cutaneous and systemic presentations. While primary cutaneous ALCL (pcALCL) has a favorable prognosis, systemic ALCL (sALCL) has poorer survival outcomes. Expression of anaplastic lymphoma kinase (ALK) by malignant cells has been suggested to distinguish sALCL from pcALCL. However, there have been documented cases of ALK-positive ALCL confined to the skin. The present study reviewed characteristics of published cutaneous ALK-positive ALCL cases to distinguish between these two entities. In 23 identified adults with ALK-positive pcALCL, 26% developed systemic involvement and 74% had skin-limited disease. In 14 pediatric patients, 36% had both cutaneous and systemic involvement and 64% had cutaneous disease only. This analysis revealed that pcALCL and sALCL could not reliably be distinguished by ALK expression or nuclear vs. cytoplasmic localization. Localized treatment with frequent monitoring may be sufficient in ALK-positive pcALCL until there is evidence of progression. Physicians should be aware of the overall spectrum of ALCL, including cutaneous limited disease, systemic disease, disease with NPM-ALK translocation, disease with ALK positivity and disease with skin recurrence.

Detection of TRAF1-ALK fusion in skin lesions of systemic ALK+ anaplastic large cell lymphoma initially involving the skin and the draining lymph node

A case of cytoplasmic anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL) initially involving the skin in a 44-year-old Japanese female is reported. The patient had a hemorrhagic erythematous tumor on the right thigh without any systemic symptoms. Pathology showed diffuse infiltration of CD30-positive anaplastic large cells positive for epithelial membrane antigen and cytoplasmic ALK. The right inguinal lymph node showed infiltration of tumor cells in the marginal sinus. Only 2 weeks after radiation therapy, the patient developed multiple subcutaneous nodules and lung involvement. Even after subsequent multichemotherapy sessions, cutaneous recurrence occurred. Literature review of cytoplasmic ALK-positive ALCL initially involving in the skin revealed that skin lesions were mostly seen in the extremities and that half of the cases developed extracutaneous lesions. Radiation and chemotherapy were effective for most cases. Inverse RT-PCR identified a tumor necrosis factor receptor-associated factor (TRAF)1-ALK fusion in our case. Most reported cases with this translocation experienced repeated changes in chemotherapy, suggesting poorer prognosis. Although ALK-positive ALCL generally responds well to chemotherapy, the presence of a TRAF1-ALK fusion may suggest resistance to treatment. Detection of fusion partners of ALK is important for predicting clinical courses and deciding treatment options.

A comparison of the International Consensus and 5th WHO classifications of T-cell lymphomas and histiocytic/dendritic cell tumours

Since the publication in 2017 of the revised 4th Edition of the World Health Organization (WHO) classification of haematolymphoid tumours, here referred to as WHO-HAEM4, significant clinicopathological, immunophenotypic and molecular advances have been made in the field of lymphomas, contributing to refining the diagnostic criteria of several diseases, upgrading entities previously defined as provisional and identifying new entities. This process has resulted in two recent classification proposals of lymphoid neoplasms: the International Consensus Classification (ICC) and the 5th edition of the WHO classification (WHO-HAEM5). In this paper, we review and compare the two classifications in terms of diagnostic criteria and entity definition, focusing on T-cell lymphomas and histiocytic/dendritic cell tumours. Moreover, we update the genetic data of the various pathological entities. The main goal is to provide a tool to facilitate the work of the pathologists, haematologists and researchers involved in the diagnosis and treatment of these haematological malignancies.

Primary cutaneous T-cell lymphoma: a review of the most common entities with focus on recent updates

Cutaneous T-cell lymphomas are an heterogeneous group of uncommon lymphoid neoplasms that are challenging to diagnose and require close collaboration between dermatologists, pathologists and hematologists/oncologists. This article reviews the most common cutaneous T-cell lymphomas: mycosis fungoides (both classic and variant forms) as well as its leukemic counterpart Sézary syndrome, CD30+ T-cell lymphoproliferative disorders including the ever-expanding group of lymphomatoid papulosis and primary cutaneous anaplastic large cell lymphoma, and primary cutaneous CD4+ small/medium lymphoproliferative disorder. We discuss the classic clinical and histopathologic features of these lymphomas and review how they can be distinguished from reactive entities. In particularly, updates to these diagnostic categories and current controversies in classification are highlighted. Moreover, we review the prognosis and treatment for each entity. These lymphomas exhibit variable prognosis, and therefore it is important to correctly classify atypical cutaneous T-cell infiltrates for appropriate patient treatment and prognosis. Cutaneous T-cell lymphomas are at the interface of several medical specialties; this review seeks to summarize key features of these lymphomas and highlight new and emerging insights into these lymphomas.

Updates in pathobiological aspects of anaplastic large cell lymphoma

Anaplastic large cell lymphomas (ALCL) encompass several distinct subtypes of mature T-cell neoplasms that are unified by the expression of CD30 and anaplastic cytomorphology. Identification of the cytogenetic abnormality t(2;5)(p23;q35) led to the subclassification of ALCLs into ALK+ ALCL and ALK- ALCL. According to the most recent World Health Organization (WHO) Classification of Haematolymphoid Tumours as well as the International Consensus Classification (ICC) of Mature Lymphoid Neoplasms, ALCLs encompass ALK+ ALCL, ALK- ALCL, and breast implant-associated ALCL (BI-ALCL). Approximately 80% of systemic ALCLs harbor rearrangement of ALK, with NPM1 being the most common partner gene, although many other fusion partner genes have been identified to date. ALK- ALCLs represent a heterogeneous group of lymphomas with distinct clinical, immunophenotypic, and genetic features. A subset harbor recurrent rearrangement of genes, including TYK2, DUSP22, and TP63, with a proportion for which genetic aberrations have yet to be characterized. Although primary cutaneous ALCL (pc-ALCL) is currently classified as a subtype of primary cutaneous T-cell lymphoma, due to the large anaplastic and pleomorphic morphology together with CD30 expression in the malignant cells, this review also discusses the pathobiological features of this disease entity. Genomic and proteomic studies have contributed significant knowledge elucidating novel signaling pathways that are implicated in ALCL pathogenesis and represent candidate targets of therapeutic interventions. This review aims to offer perspectives on recent insights regarding the pathobiological and genetic features of ALCL.

Primary Cutaneous Anaplastic Large Cell Lymphoma-A Review of Clinical, Morphological, Immunohistochemical, and Molecular Features

Primary cutaneous anaplastic large cell lymphoma (ALCL) is the second most common cutaneous T-cell lymphoma after mycosis fungoides and belongs to the spectrum of cutaneous CD30+ T-cell lymphoproliferative disorders. Although primary cutaneous ALCL usually presents as a localized nodule or papule with or without ulceration, multifocal lesions may occur in up to 20% of cases. Histologically, primary cutaneous ALCL consists of a diffuse dermal infiltrate of medium to large anaplastic/pleomorphic cells with abundant amphophilic-to-eosinophilic cytoplasm, horseshoe-shaped nuclei, strong and diffuse expression of CD30, and with focal or no epidermotropism. The neoplastic infiltrate may show angiocentric distribution and may extend to the subcutis. Patients with localized or multifocal disease have a similar prognosis with a 10-year overall survival rate of 90%. Approximately 30% of primary cutaneous ALCLs harbor a DUSP22 (6p25.3) gene rearrangement that results in decreased expression of this dual-specific phosphatase, decreased STAT3 activation, and decreased activity of immune and autoimmune-mediated mechanisms regulated by T-cells.

Primary cutaneous T-cell lymphoma: a review of the most common entities with focus on recent updates

Cutaneous T-cell lymphomas are an heterogeneous group of uncommon lymphoid neoplasms that are challenging to diagnose and require close collaboration between dermatologists, pathologists and hematologists/oncologists. This article reviews the most common cutaneous T-cell lymphomas: mycosis fungoides (both classic and variant forms) as well as its leukemic counterpart Sézary syndrome, CD30+ T-cell lymphoproliferative disorders including the ever-expanding group of lymphomatoid papulosis and primary cutaneous anaplastic large cell lymphoma, and primary cutaneous CD4+ small/medium lymphoproliferative disorder. We discuss the classic clinical and histopathologic features of these lymphomas and review how they can be distinguished from reactive entities. In particularly, updates to these diagnostic categories and current controversies in classification are highlighted. Moreover, we review the prognosis and treatment for each entity. These lymphomas exhibit variable prognosis, and therefore it is important to correctly classify atypical cutaneous T-cell infiltrates for appropriate patient treatment and prognosis. Cutaneous T-cell lymphomas are at the interface of several medical specialties; this review seeks to summarize key features of these lymphomas and highlight new and emerging insights into these lymphomas.

Diagnosis and management of cutaneous lymphomas and lymphoid proliferations in children, adolescents and young adults (CAYA)

Cutaneous lymphomas and lymphoid proliferations (LPD) in children, adolescents, and young adults (CAYA) are a heterogeneous group of lymphoid neoplasms that present formidable diagnostic challenges to clinicians and pathologists alike. Although rare overall, cutaneous lymphomas/LPD occur in real-world settings and awareness of the differential diagnosis, potential complications, and various therapeutic approaches will help ensure the optimal diagnostic work-up and clinical management. Lymphomas/LPD involving the skin can occur as primary cutaneous disease in a patient that characteristically has lymphoma/LPD confined to the skin, or as secondary involvement in patients with systemic disease. This review will comprehensively summarize both primary cutaneous lymphomas/LPD that occur in the CAYA population as well as those CAYA systemic lymphomas/LPD with propensity for secondary cutaneous involvement. Focus on the most common primary entities occurring in CAYA will include lymphomatoid papulosis, primary cutaneous anaplastic large cell lymphoma, mycosis fungoides, subcutaneous panniculitis-like T-cell lymphoma, and hydroa vacciniforme lymphoproliferative disorder.

Diagnosis and management of ALK-positive anaplastic large cell lymphoma in children and adolescents

Anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL) is a CD30-positive T cell lymphoma characterized by signalling from constitutively activated ALK fusion proteins. Most children and adolescents present in advanced stages, often with extranodal disease and B symptoms. The current front-line therapy standard of six cycles polychemotherapy reaches an event-free survival of 70%. The strongest independent prognostic factors are minimal disseminated disease and early minimal residual disease. At relapse, ALK-inhibitors, Brentuximab Vedotin, Vinblastine, or second line chemotherapy are effective re-inductions. Survival at relapse exceeds 60-70% with consolidation according to the time of relapse (Vinblastine monotherapy or allogeneic hematopoietic stem cell transplantation) so that the overall survival reaches 95%. It needs to be shown whether check-point inhibitors or long-term ALK-inhibition may substitute for transplantation. The future necessitates international cooperative trials testing whether a shift of paradigm to a chemotherapy-free regimen can cure ALK-positive ALCL.

Recent advances in cutaneous lymphoma-implications for current and future classifications

The Revised European-American Classification of mature lymphoid neoplasms published in 1994 and the 2001, 2008 and 2016 WHO classifications that followed, were the product of international collaboration and consensus amongst haematopathologists, geneticists, molecular scientists and clinicians. Primary cutaneous lymphomas were fully incorporated into this process following the publication of the WHO-EORTC classification of cutaneous lymphomas in 2005. The definition, diagnostic criteria and recommended studies for primary cutaneous lymphoma continue to be refined. The 2022 International Consensus Classification represents the most recent update and an overview of all the main entities presenting primarily in the skin, together with the major changes in classification, are summarized herein. Primary cutaneous marginal zone lymphoma is segregated from other extranodal marginal zone lymphomas of mucosa-associated lymphoid tissue (MALT lymphoma) and downgraded to a lymphoproliferative disorder in line with its markedly indolent behaviour. In addition, two subtypes are recognised, based largely but not exclusively on whether they are heavy chain class-switched or IgM positive. Similarly, in keeping with a trend to greater conservatism, primary cutaneous acral CD8 positive T cell lymphoma is now also classified as a lymphoproliferative disorder. In addition, significant new insights into the biology of primary cutaneous lymphoma have also recently been forthcoming and will be presented. These studies have enhanced our knowledge of genetic, epigenetic and transcriptional changes in this group of diseases. They not only identify potential targets for novel therapies, but also raise as yet unanswered questions as to how we categorise cutaneous lymphomas, particularly with respect to relationships with similar lymphomas at extracutaneous sites.

Aggressive Primary Cutaneous Anaplastic T-Cell Lymphoma Successfully Treated with Autologous Stem Cell Transplant and Brentuximab Vedotin Consolidation: Case Report and Review of the Literature

Primary cutaneous CD30+ lymphoproliferative disorders include primary cutaneous anaplastic large cell lymphoma (pcALCL) and lymphomatoid papulosis. The prognosis of the disease is usually excellent but, in a minority of cases, it presents with extracutaneous involvement and aggressive behavior. The case we present—relapsed after surgical excision, immunosuppressive therapy, and conventional chemotherapy—is the first one treated with Autologous Stem Cell transplant followed by Brentuximab Vedotin consolidation, a scheme already used for high risk Hodgkin Lymphoma.

Pediatric Cutaneous Hematologic Disorders: Cutaneous Lymphoma and Leukemia Cutis: Experience of a Tertiary-Care Pediatric Institution and Review of the Literature

BACKGROUND

Cutaneous hematologic malignancies are rare in children, and the literature about them is still sparse.

OBJECTIVE

The purpose of our study was to report our experience with pediatric cases of cutaneous hematologic disorders and describe their clinical and histological features.

METHODS

Data were retrospectively collected from the histopathologic database of the CHU Sainte-Justine, University of Montreal, Montreal, Canada. All patients up to 18 years of age with a diagnosis of a primary cutaneous lymphoma (including lymphomatoid papulosis), secondary cutaneous lymphoma or cutaneous manifestations of leukemia, followed from 1980 to 2019 at our center were reviewed.

RESULTS

Thirty-six patients were included. Age at presentation ranged from birth to 18 years of age (mean 7.83 ± 5.16; median 7.0). Ten different hematologic disorders were identified according to the WHO-EORTC classifications: lymphomatoid papulosis (10 cases), mycosis fungoides (6 cases), anaplastic large cell lymphoma (4 cases), pre-B acute lymphoid leukemia (5 cases), primary cutaneous marginal zone B-cell lymphoma (4 cases), primary cutaneous CD4⁺medium T-cell lymphoproliferative disorder (1 case), extranodal NK/T-cell lymphoma (1 case), hydroa vacciniforme-like lymphoproliferative disorder (1 case), B-cell lymphoblastic lymphoma (1 case) and acute myeloid leukemia (3 cases).

CONCLUSION

The most common subtype of cutaneous hematologic disease in our single institution study was lymphomatoid papulosis (type A and type C), followed by mycosis fungoides. Recognition of this large clinical and histological spectrum by dermatologists is important because diagnosis is often established by biopsy of skin lesions, even in secondary cutaneous cases. Moreover, the clinicopathological correlation is of utmost importance for the final diagnosis of those pathologies.

Genetic and epigenetic insights into cutaneous T-cell lymphoma

Primary cutaneous T-cell lymphomas (CTCL) constitute a heterogeneous group of non-Hodgkin T-cell lymphomas that present in the skin. In recent years significant progress has been made in the understanding of the pathogenesis of CTCL. Progress in CTCL classifications combined with technical advances, in particular next generation sequencing (NGS), enabled a more detailed analysis of the genetic and epigenetic landscape and transcriptional changes in clearly defined diagnostic entities. These studies not only demonstrated extensive heterogeneity between different CTCL subtypes but also identified recurrent alterations that are highly characteristic for diagnostic subgroups of CTCL. The identified alterations in particular involve epigenetic remodelling, cell cycle regulation, and the constitutive activation of targetable, oncogenic pathways. In this respect, aberrant JAK-STAT signaling is a recurrent theme, however not universal for all CTCL and with seemingly different underlaying causes in different entities. A number of the mutated genes identified are potentially actionable targets for the development of novel therapeutic strategies. Moreover, these studies have produced an enormous amount of information that will be critically important for the further development of improved diagnostic and prognostic biomarkers that can assist in the clinical management of CTCL patients. In the present review the main findings of these studies in relation to their functional impact on the malignant transformation process are discussed for different subtypes of CTCL.

ALK-Negative Anaplastic Large Cell Lymphoma: Current Concepts and Molecular Pathogenesis of a Heterogeneous Group of Large T-Cell Lymphomas

Simple Summary

ALK- anaplastic large cell lymphoma (ALK- ALCL) is a rare subtype of CD30+ large T-cell lymphoma that typically affects older adults and has a poor prognosis. Recognition of its histopathologic spectrum, subtypes, and of other tumors that can resemble ALK- ALCL is crucial to avoid making a wrong diagnosis that could result in inappropriate treatment for a patient. In recent years, several important studies have identified recurrent molecular alterations that have shed light on the pathogenesis of this lymphoma. However, on the other hand, putting all this vast information together into a concise form has become challenging. In this review, we present not only a more detailed view of the histopathologic findings of ALK- ALCL but also, we attempt to provide a more simplified perspective of the relevant genetic and molecular alterations of this type of lymphoma, that in our opinion, is not available to date.

Abstract

Anaplastic large cell lymphoma (ALCL) is a subtype of CD30+ large T-cell lymphoma (TCL) that comprises ~2% of all adult non-Hodgkin lymphomas. Based on the presence/absence of the rearrangement and expression of anaplastic lymphoma kinase (ALK), ALCL is divided into ALK+ and ALK-, and both differ clinically and prognostically. This review focuses on the historical points, clinical features, histopathology, differential diagnosis, and relevant cytogenetic and molecular alterations of ALK- ALCL and its subtypes: systemic, primary cutaneous (pc-ALCL), and breast implant-associated (BIA-ALCL). Recent studies have identified recurrent genetic alterations in this TCL. In systemic ALK- ALCL, rearrangements in DUSP22 and TP63 are detected in 30% and 8% of cases, respectively, while the remaining cases are negative for these rearrangements. A similar distribution of these rearrangements is seen in pc-ALCL, whereas none have been detected in BIA-ALCL. Additionally, systemic ALK- ALCL—apart from DUSP22-rearranged cases—harbors JAK1 and/or STAT3 mutations that result in the activation of the JAK/STAT signaling pathway. The JAK1/3 and STAT3 mutations have also been identified in BIA-ALCL but not in pc-ALCL. Although the pathogenesis of these alterations is not fully understood, most of them have prognostic value and open the door to the use of potential targeted therapies for this subtype of TCL.

Primary cutaneous T-cell lymphomas in childhood and adolescence

Primary cutaneous lymphomas are extranodal non-Hodgkin lymphomas of T- or B- cell origin, that predominantly affect older patients but have been reported in all age groups and as early as in the first years of life. Diagnosis of cutaneous lymphomas is challenging and requires high clinical suspicion and close collaboration between dermatologists, pediatric oncologists and pathologists. Skin involvement of non-Hodgkin lymphomas in children or adolescents can either be primary cutaneous or secondary due to an underlying nodal lymphoma. The most common primary cutaneous lymphomas encountered in children are of T-cell origin, with mycosis fungoides being the most prevalent cutaneous T-cell lymphoma, followed by CD30⁺ lymphoproliferative disorders. While cutaneous lymphomas share clinicopathologic characteristics between juvenile and adult forms, there are important differences in terms of clinical presentation, diagnosis and treatment. The hypopigmented variant of mycosis fungoides seems to be overrepresented in the pediatric age group. Prognosis and treatment of mycosis fungoides are stage dependent. The majority of children present with early-stage disease and respond well to topical corticosteroids and phototherapy.

Update on Pediatric and Young Adult Mature Lymphomas

After acute leukemia and brain and central nervous system tumors, mature lymphomas represent the third most common cancer in pediatric patients. Non-Hodgkin lymphoma accounts for approximately 60% of lymphoma diagnoses in children, with the remainder representing Hodgkin lymphoma. Among non-Hodgkin lymphomas in pediatric patients, aggressive lymphomas, such as Burkitt lymphoma, diffuse large B-cell lymphoma, and anaplastic large cell lymphoma, predominate. This article summarizes the epidemiologic, histopathologic, and molecular features of selected mature systemic B-cell and T-cell lymphomas encountered in this age group.

Pediatric primary cutaneous anaplastic large cell lymphoma treated with brachytherapy

Primary cutaneous anaplastic large cell lymphoma (PC-ALCL) is a CD30+ lymphoproliferative disorder that rarely occurs in children. Although there are currently no consensus guidelines for the treatment of cutaneous lymphoma in the pediatric population, the isolated form of PC-ALCL is typically managed by surgical excision or external beam radiation therapy. We report the case of a 6-year-old girl with primary cutaneous anaplastic large cell lymphoma that was treated with brachytherapy with no recurrence after 21 months of follow-up, suggesting that brachytherapy may be considered as a treatment for pediatric cutaneous large cell anaplastic lymphoma.

Primär kutane T‐Zell‐Lymphome im Kindes‐ und Jugendalter

Primär kutane Lymphome sind extranodale T- oder B-Zell-Non-Hodgkin-Lymphome, die vorwiegend ältere Patienten betreffen, aber in allen Altersgruppen einschließlich der ersten Lebensjahre auftreten können. Die Diagnose kutaner Lymphome ist eine Herausforderung und erfordert einen hohen klinischen Verdacht sowie enge Zusammenarbeit zwischen Dermatologen, pädiatrischen Onkologen und Pathologen. Generell müssen primär kutane Lymphome von sekundär kutanen Lymphomen, welche meist von nodalen oder extranodalen Lymphomen ausgehen, unterschieden werden. Die häufigsten primär kutanen Lymphome im Kindesalter sind T-Zell Lymphome, wobei Mycosis fungoides das häufigste kutane T-Zell-Lymphom darstellt, gefolgt von CD30+ lymphoproliferativen Erkrankungen. Während klinisch-pathologische Merkmale kutaner Lymphome bei Jugendlichen und Erwachsenen ähnlich sind, gibt es wichtige Unterschiede bezüglich klinischer Präsentation, Diagnose und Behandlung. Die hypopigmentierte Variante der Mycosis fungoides scheint in der pädiatrischen Altersgruppe überrepräsentiert zu sein. Prognose und Behandlung der Mycosis fungoides sind stadienabhängig. Die Mehrheit der Kinder weist ein frühes Krankheitsstadium auf und spricht gut auf topische Kortikosteroide und Phototherapie an.

How I Diagnose Anaplastic Large Cell Lymphoma

OBJECTIVES

This review describes our approach to the diagnosis of all 4 anaplastic large cell lymphoma (ALCL) entities.

METHODS

ALCLs are a group of CD30-positive mature T-cell lymphomas with similar morphologic and phenotypic characteristics but variable clinical and genetic features. They include systemic ALK-positive ALCL, systemic ALK-negative ALCL, primary cutaneous ALCL, and the recently described provisional entity breast implant-associated ALCL.

RESULTS

In cases with classic features, the diagnosis of ALCL is often straightforward. However, variant histology, the importance of clinical history, and multiple antigenic aberrancies all present challenges to accurate diagnosis and subclassification.

CONCLUSIONS

A systematic approach to the diagnosis of ALCL and awareness of potential mimics are critical to avoid misdiagnosis. It is also crucial to correctly identify localized forms of ALCL to avoid classification as systemic ALCL and subsequent overtreatment.

Clinical, Histologic, and Molecular Characteristics of Anaplastic Lymphoma Kinase-positive Primary Cutaneous Anaplastic Large Cell Lymphoma

Unlike systemic anaplastic large cell lymphoma, the vast majority of primary cutaneous anaplastic large cell lymphomas (C-ALCL) do not carry translocations involving the ALK gene and do not express ALK. Expression of ALK protein therefore strongly suggests secondary cutaneous involvement of a systemic anaplastic large cell lymphoma. Recent studies described a small subgroup of ALK-positive C-ALCL, but information on frequency, prognosis, and translocation partners is virtually lacking. A total of 6/309 (2%) C-ALCL patients included in the Dutch registry for cutaneous lymphomas between 1993 and 2019 showed immunohistochemical ALK expression. Clinical and histopathologic characteristics, immunophenotype and disease course were evaluated. Underlying ALK translocations were analyzed with anchored multiplex polymerase chain reaction-based targeted next-generation sequencing. Median age at diagnosis was 39 years (range: 16 to 53 y). All patients presented with a solitary lesion. Treatment with radiotherapy (n=5) or anthracycline-based chemotherapy (n=1) resulted in complete responses in all 6 patients. Three patients developed a relapse, of whom 2 extracutaneous. After a median follow-up of 41 months, 5 patients were alive without disease and 1 patient died of lymphoma. Immunohistochemically, 3 cases (50%) showed combined nuclear and cytoplasmic ALK expression with underlying NPM1-ALK fusions, while 3 cases (50%) showed solely cytoplasmic ALK expression with variant ALK fusion partners (TRAF1, ATIC, TPM3). ALK-positive C-ALCL is extremely uncommon, has a comparable favorable prognosis to ALK-negative C-ALCL, and should be treated in the same way with radiotherapy as first-line treatment.

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.

Recurrent Oncogenic JAK and STAT Alterations in Cutaneous CD30-Positive Lymphoproliferative Disorders

The group of cutaneous CD30-positive lymphoproliferative disorders (LPD) comprises two different entities, namely lymphomatoid papulosis (LyP) and cutaneous anaplastic large T-cell lymphoma (cALCL). LyP constitutes a benign lymphoproliferation with spontaneously regressing papules, whereas cALCL presents with solitary or multiple skin tumors with a low propensity to disseminate. To elucidate the hitherto largely unknown molecular pathogenesis of these entities, we performed comprehensive next-generation sequencing in a well-characterized cohort of 12 patients. Considering the low tumor cell content of LyP, we applied targeted sequencing technologies with a hybrid capture-based DNA library preparation approach and for the identification of fusion transcripts an anchored multiplex PCR enrichment kit. As the major finding, we detected, in 50% of LPD, genetic events that implied a constitutively activated Janus kinase-signal transducer and activator of transcription signaling (JAK-STAT) pathway in these entities. The identified molecular aberrations comprised either pathogenic STAT mutations or oncogenic fusion transcripts comprising effector domains of JAK. With respect to LyP, we report to our knowledge such previously unreported genetic aberrations in this specific entity. The detection of these convergent aberrations within the JAK-STAT signaling pathway deciphers common potential driving mechanisms of lymphomagenesis within LPD being shared between LyP and cALCL. Moreover, the presence of these oncogenic alterations paves the way to develop novel personalized treatment strategies.

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.

Pathology and genetics of anaplastic large cell lymphoma

Anaplastic large cell lymphomas are a rare subtype of peripheral/mature T-cell lymphomas which are clinically, pathologically and genetically heterogeneous. Both ALK-positive (ALK+) and ALK-negative (ALK-) ALCL are composed of large lymphoid cells with abundant cytoplasm and pleomorphic features with horseshoe-shaped and reniform nuclei. ALK+ ALCL were considered as a definite entity in the 2008 World Health Organization classification of hematopoietic and lymphoid tissues. ALK-ALCL was included as a provisional entity in the WHO 2008 edition and in the most recent 2017 edition, it is now considered a distinct entity that includes cytogenetic subsets that appear to have prognostic implications (e.g. 6p25 rearrangements at IRF4/DUSP22 locus). ALK+ ALCLs are distinct in epidemiology and pathogenetic origin and should be distinguished from ALK-ALCL, cutaneous ALCL and breast implant associated ALCL which have distinct clinical course and pathogenetic features. Breast implant-associated ALCL is now recognized as a new provisional entity distinct from other ALK-ALCL; notably that it is a noninvasive disease associated with excellent outcome. In this article, we will provide an overview of the salient themes relevant to the pathology and genetic mechanisms in ALCL.

ALCL by any other name: the many facets of anaplastic large cell lymphoma

Anaplastic large cell lymphomas (ALCLs) encompass a group of CD30(+) non-Hodgkin T-cell lymphomas. While the different subtypes of ALCLs may share overlapping clinical patient demographics as well as histological and immunohistochemical phenotypes, these tumours can drastically differ in clinical behaviour and genetic profiles. Currently, four distinct ALCL entities are recognised in the 2016 WHO classification: anaplastic lymphoma kinase (ALK)(+), ALK(-), primary cutaneous and breast implant-associated. ALK(+) ALCL demonstrates a spectrum of cell cytology ranging from small to large lymphoma cells and characteristic 'hallmark' cells. ALK(+) ALCL consistently demonstrates ALK gene rearrangements and carries a favourable prognosis. ALK(-) ALCL morphologically and immunohistochemically mimics ALK(+) ALCL but lacks the ALK gene rearrangement. ALK(-) ALCLs are associated with variable prognoses depending on specific gene rearrangements; while DUSP22-rearranged cases have favourable outcomes similar to ALK(+) ALCLs, cases with p63 rearrangements carry a dismal prognosis and 'triple-negative' cases (those lacking ALK, DUSP22 and TP63 rearrangements) have an intermediate prognosis. Primary cutaneous ALCL presents as a skin lesion, lacks the ALK gene translocation and carries a favourable prognosis, similar or superior to ALK(+) ALCL. Breast implant-associated ALCL presents as a seroma with a median of 8-10 years after implant placement, lacks the ALK gene translocation and has an overall favourable but variable prognosis, depending on extent of disease at diagnosis and treatment. In this review, we present the clinical, pathological and genetic features of the ALCLs with emphasis on practical points and differential diagnoses for practising pathologists.

Lymphomatoid papulosis: an update and review

Lymphomatoid papulosis (LyP) is a benign chronic often relapsing skin condition that belongs to the CD30-positive cutaneous lymphoproliferative disorders. LyP typically presents as crops of lesions with a tendency to self-resolve, and morphology can range from solitary to agminated or diffuse papules and plaques to nodules or tumours. The clinical-histological spectrum can range from borderline cases to overlap with primary cutaneous anaplastic cell lymphoma (pcALCL). Histology and immunophenotype commonly show overlap with other CD30-positive disorders and sometimes may be identical to pcALCL, making its diagnosis more difficult. Patients with LyP have an increased risk of developing a second neoplasm such as mycosis fungoides, pcALCL and/or Hodgkin lymphoma. Clinical correlation allows its proper classification and diagnosis, which is fundamental for treatment and prognosis. This review focuses on the clinical appearance, histopathological features, diagnosis, differential diagnosis and management of LyP.

The 2018 update of the WHO-EORTC classification for primary cutaneous lymphomas

Primary cutaneous lymphomas are a heterogeneous group of T- and B-cell lymphomas that present in the skin with no evidence of extracutaneous disease at the time of diagnosis. The 2005 World Health Organization-European Organization for Research and Treatment of Cancer (WHO-EORTC) consensus classification has served as a golden standard for the diagnosis and classification of these conditions. In September 2018, an updated version of the WHO-EORTC was published in the fourth edition of the WHO Classification of Skin Tumours Blue Book. In this classification, primary cutaneous acral CD8⁺ T-cell lymphoma and Epstein-Barr virus positive (EBV⁺) mucocutaneous ulcer are included as new provisional entities, and a new section on cutaneous forms of chronic active EBV disease has been added. The term "primary cutaneous CD4⁺ small/medium T-cell lymphoma" was modified to "primary cutaneous CD4⁺ small/medium T-cell lymphoproliferative disorder" because of its indolent clinical behavior and uncertain malignant potential. Modifications have also been made in the sections on lymphomatoid papulosis, increasing the spectrum of histologic and genetic types, and primary cutaneous marginal zone lymphomas recognizing 2 different subtypes. Herein, the characteristic features of these new and modified entities as well as the results of recent molecular studies with diagnostic, prognostic, and/or therapeutic significance for the different types of primary cutaneous lymphomas are reviewed. An update of the frequency and survival of the different types of primary cutaneous lymphomas is provided.

CD30-positive primary cutaneous lymphoproliferative disorders: molecular alterations and targeted therapies

Primary cutaneous CD30-positive T-cell lymphoproliferative disorders are the second most common subgroup of cutaneous T-cell lymphomas. They include two clinically different entities with some overlapping features and borderline cases: lymphomatoid papulosis and primary cutaneous anaplastic large cell lymphoma. Molecular studies of primary cutaneous anaplastic large cell lymphoma reveal an increasing level of heterogeneity that is associated with histological and immunophenotypic features of the cases and their response to specific therapies. Here, we review the most significant genetic, epigenetic and molecular alterations described to date in primary cutaneous CD30-positive T-cell lymphoproliferative disorders, and their potential as therapeutic targets.

Molecular profiling reveals immunogenic cues in anaplastic large cell lymphomas with DUSP22 rearrangements

Anaplastic large cell lymphomas (ALCLs) are CD30-positive T-cell non-Hodgkin lymphomas broadly segregated into ALK-positive and ALK-negative types. Although ALK-positive ALCLs consistently bear rearrangements of the ALK tyrosine kinase gene, ALK-negative ALCLs are clinically and genetically heterogeneous. About 30% of ALK-negative ALCLs have rearrangements of DUSP22 and have excellent long-term outcomes with standard therapy. To better understand this group of tumors, we evaluated their molecular signature using gene expression profiling. DUSP22-rearranged ALCLs belonged to a distinct subset of ALCLs that lacked expression of genes associated with JAK-STAT3 signaling, a pathway contributing to growth in the majority of ALCLs. Reverse-phase protein array and immunohistochemical studies confirmed the lack of activated STAT3 in DUSP22-rearranged ALCLs. DUSP22-rearranged ALCLs also overexpressed immunogenic cancer-testis antigen (CTA) genes and showed marked DNA hypomethylation by reduced representation bisulfate sequencing and DNA methylation arrays. Pharmacologic DNA demethylation in ALCL cells recapitulated the overexpression of CTAs and other DUSP22 signature genes. In addition, DUSP22-rearranged ALCLs minimally expressed PD-L1 compared with other ALCLs, but showed high expression of the costimulatory gene CD58 and HLA class II. Taken together, these findings indicate that DUSP22 rearrangements define a molecularly distinct subgroup of ALCLs, and that immunogenic cues related to antigenicity, costimulatory molecule expression, and inactivity of the PD-1/PD-L1 immune checkpoint likely contribute to their favorable prognosis. More aggressive ALCLs might be pharmacologically reprogrammed to a DUSP22-like immunogenic molecular signature through the use of demethylating agents and/or immune checkpoint inhibitors.

Primary Pediatric Cutaneous T-Cell Lymphoproliferative Disorders: 3 New Cases

Primary cutaneous lymphoproliferative disorders are a composite group of diseases with considerable differences in histopathologic, immunophenotypic, and clinical features. They are exceedingly rare in children and in the literature only few cases are reported with extremely different therapeutic approaches. Because of the rarity of cutaneous lymphomas we consider crucial to increase the knowledge of these diseases providing every single case. We present 3 pediatric cases of primary cutaneous T-cell lymphomas occurred to our center with different features and therapeutic approach.

Cutaneous Hematolymphoid and Histiocytic Proliferations in Children

This article focuses on cutaneous hematopoietic neoplasms that are more likely to be encountered in the pediatric age-group and includes both lymphoproliferative and histiocytic disorders. The cutaneous hematologic disorders in children have a different epidemiologic profile to what is seen during adulthood. Although mycosis fungoides is the most frequent form of cutaneous lymphoma in adults, it is very rare in children. Because lymphoblastic leukemias and lymphomas are more frequent in the pediatric setting, cutaneous leukemic infiltrates are relatively common in this age-group. Similarly, histiocytic disorders are more common in children, particularly Langerhans cell histiocytosis and juvenile xanthogranuloma. Notably, the histiocytic disorders have undergone significant modifications on their nomenclature in the basis of the molecular characteristics that are present in them. A summary of the most frequent cutaneous hematopoietic disorders in children will be discussed further in this review.

Primary cutaneous anaplastic large-cell lymphoma: A case report

RATIONALE

Primary cutaneous anaplastic large-cell lymphoma (C-ALCL) is a rare cancer belonging to the group of primary T-cell lymphoproliferative diseases. C-ALCL is characterized by the presence of single or multiple ulcerated lesions on the skin's surface.

PATIENT CONCERNS

This is the case of a 73-year-old man who reported to the Clinic of Cranio-Maxillofacial and Oral Surgery and Implantology, Medical University of Warsaw, owing to a skin tumor in the right parotideomasseteric region, initially diagnosed as discoid lupus erythematosus. During treatment for discoid lupus erythematosus, biopsy was repeated because of significant disease progression and dynamic tumor growth. Histopathological examination revealed the presence of pilomatrix carcinoma (trichilemmal carcinoma). Because of the discrepancy between clinical and histopathological findings, the tumor specimen was submitted to another facility, wherein lymphoma infiltration by anaplastic large cells was found in the dermis and subcutaneous tissue.

DIAGNOSIS

C-ALCL.

INTERVENTIONS

The patient was transferred to the Lymphoid Tumours Clinic of the Maria Skłodowska Curie Memorial Cancer Centre and Institute of Oncology in Warsaw, where chemotherapy was initiated.

OUTCOMES

After 4 cycles of chemotherapy, a complete remission of skin lesions was achieved. During the 5-year follow-up, no recurrence occurred.

LESSONS

C-ALCL is a rare type of cancer. Misdiagnosis can lead to inappropriate therapy and result in disease progression or unnecessary harm to the patient.

ALK-positive primary cutaneous anaplastic large cell lymphoma: a case report and review of the literature

Anaplastic large cell lymphoma (ALCL) limited to the skin is a distinct disease that is designated primary cutaneous ALCL (pcALCL). It has an indolent course with a significantly better prognosis compared to systemic ALCL (sALCL). Anaplastic lymphoma kinase (ALK) expression in lesions of cutaneous ALCL is classically considered to be a marker for skin involvement by sALCL. However, recent reports of patients with ALK-positive pcALCL challenge this concept and raise prognostic and therapeutic dilemmas. Herein, we report a case of ALK-positive pcALCL in a 45-year-old woman who was treated with local radiotherapy. We review previously reported cases in the literature to better characterize this rare variant. Overall, the rates of cutaneous recurrence, systemic dissemination, and disease-related mortality in ALK-positive pcALCL do not differ from those previously reported in pcALCL. ALK-positive pcALCL is diagnosed at younger age and has a better disease course in children compared to adults with lower incidences of skin recurrence and progression to systemic disease. We conclude that ALK-positivity in cutaneous ALCL does not necessarily imply systemic disease. ALK-positive pcALCL has an excellent prognosis and should be treated by excision and/or radiotherapy. However, patients must remain under close long-term follow-up as recurrence and progression to systemic disease may occur.

Anaplastic Lymphoma Kinase in Cutaneous Malignancies

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase that has been implicated in the pathogenesis of a variety of neoplasms. As suggested by its name, ALK was first described as part of a translocation product in cases of anaplastic large-cell lymphoma, with other genetic and cytogenetic ALK mutations subsequently coming to attention in the development of many other hematologic and solid organ malignancies. ALK has now been shown to play a role in the pathogenesis of several cutaneous malignancies, including secondary cutaneous systemic anaplastic large-cell lymphoma (ALCL) and primary cutaneous ALCL, melanoma, spitzoid tumors, epithelioid fibrous histiocytoma, Merkel cell carcinoma, and basal cell carcinoma. The characterization of ALK-positivity in these cutaneous malignancies presents exciting opportunities for utilizing ALK-targeted inhibitors in the treatment of these diseases.

Genetic Landscape and Classification of Peripheral T Cell Lymphomas

PURPOSE OF REVIEW

Peripheral T cell lymphomas (PTCLs) are markedly heterogeneous at the clinical, pathological, and molecular levels. This review will discuss genetic findings in PTCL with special emphasis on how they impact lymphoma classification.

RECENT FINDINGS

Sequencing studies have identified recurrent genetic alterations in nearly every PTCL subtype. In anaplastic large cell lymphoma, these studies have revealed novel chromosomal rearrangements and mutations that have prognostic significance and may suggest new therapeutic approaches. Angioimmunoblastic T cell lymphoma has been found to have mutations overlapping some cases of PTCL, not otherwise specified with a T follicular helper cell phenotype. Across various subtypes, recurrent mutations and structural alterations affecting genes involved in epigenetic regulation, T cell receptor signaling, and immune response may represent targets for precision therapy approaches. New genetic findings are refining the classification of PTCLs and are beginning to be used clinically for diagnosis, risk stratification, and individualized therapy.

Primary cutaneous anaplastic large cell lymphoma

Primary cutaneous anaplastic large cell lymphoma (PC-ALCL) is a CD30+ lymphoproliferative disorder (LPD) of the skin with a relatively good prognosis in the absence of high-stage disease. CD30+ LPDs comprise approximately 25%-30% of primary cutaneous lymphomas and as a group represent the second most common clonal T-cell neoplasm of the skin behind mycosis fungoides. Diagnosis of PC-ALCL relies strongly on clinicopathologic correlation given the potential morphologic, clinical and molecular overlap with the other cutaneous CD30+ LPD, lymphomatoid papulosis, and more aggressive hematolymphoid neoplasms.

A new era for cutaneous CD30-positive T-cell lymphoproliferative disorders

Cutaneous CD30+ T-cell lymphoproliferative disorders (CD30+ T-LPD) represent a spectrum encompassing lymphomatoid papulosis (LyP), primary cutaneous anaplastic large-cell lymphoma (pcALCL) and borderline lesions. They share the expression of CD30 as a common phenotypic marker. They differ however in their clinical presentation, the histological features and clinical course. Moreover, LyP and PcALCL show numerous clinical, histological and phenotypic variants. Overlapping features of LyP and pcALCL with themselves and with other cutaneous and systemic lymphomas emphasize the importance of careful clinicopathologic correlation and staging in the diagnosis of CD30+ T-LPD. Furthermore, an increasing number of inflammatory and infectious skin disorders harboring medium-sized to large CD30+ cells have to be considered in the differential diagnosis. Whereas the expression of CD30 in cutaneous CD30+ T-LPD stands for a favourable prognosis, its expression in other cutaneous and systemic lymphomas has a divergent impact. The assessment of CD30 expression does not only provide prognostic information, but is of potential therapeutic relevance as CD30 can serve as a therapeutic target. This review focuses on the clinicopathological and phenotypic spectrum of CD30+ T-LPD, its differential diagnoses and the role of CD30 as a diagnostic, prognostic and therapeutic marker.

Pediatric case of anaplastic lymphoma kinase-positive anaplastic large cell lymphoma forming a solitary skin tumor on the forearm

A 5-year-old girl noticed a rapidly growing reddish nodule on her right forearm. Although oral antibiotics had been administrated for 2 weeks, the tumor enlarged. Skin biopsy revealed excessive infiltration of atypical neoplastic cells expressing CD4, CD30 and anaplastic lymphoma kinase (ALK). These histological and immunohistochemical findings were consistent with anaplastic large cell lymphoma (ALCL). Computed tomography showed multiple lymphadenopathy, but lymph node biopsy and bone marrow examination did not show any evidence of systemic dissemination. However, due to the positive results for ALK and multiple lymphadenopathy, we diagnosed ALK-positive ALCL forming a solitary skin tumor on the forearm. The patient received chemotherapy and presented marked improvement. This paper discusses the difficulty of diagnosing pediatric ALK-positive ALCL limited to the skin and reviews the medical published work.