The majority of cutaneous marginal zone B-cell lymphomas expresses class-switched immunoglobulins and develops in a T-helper type 2 inflammatory environment

Cutaneous B-cell lymphomas: 2023 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Approximately one-fourth of primary cutaneous lymphomas are B-cell derived and are generally classified into three distinct subgroups: primary cutaneous follicle center lymphoma (PCFCL), primary cutaneous marginal zone lymphoma (PCMZL), and primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL, LT).

DIAGNOSIS

Diagnosis and disease classification is based on histopathologic review and immunohistochemical staining of an appropriate skin biopsy. Pathologic review and an appropriate staging evaluation are necessary to distinguish primary cutaneous B-cell lymphomas from systemic B-cell lymphomas with secondary skin involvement.

RISK-STRATIFICATION

Disease histopathology remains the most important prognostic determinant in primary cutaneous B-cell lymphomas. Both PCFCL and PCMZL are indolent lymphomas that infrequently disseminate to extracutaneous sites and are associated with 5-year survival rates that exceed 95%. In contrast, PCDLBCL, LT is an aggressive lymphoma with an inferior prognosis.

RISK-ADAPTED THERAPY

PCFCL and PCMZL patients with solitary or relatively few skin lesions may be effectively managed with local radiation therapy. While single-agent rituximab may be employed for patients with more widespread skin involvement, multiagent chemotherapy is rarely appropriate. In contrast, management of patients with PCDLBCL, LT is comparable to the management of patients with systemic DLBCL.

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.

Disease-Defining Molecular Features of Primary Cutaneous B-Cell Lymphomas: Implications for Classification and Treatment

Primary cutaneous B-cell lymphoma-primary cutaneous follicle center lymphoma; primary cutaneous marginal zone lymphoma; and primary cutaneous diffuse large B-cell, leg type-is a heterogeneous group with a variety of clinical and histological presentations. Until recently, the molecular bases of these disease subtypes have been unclear. We and others have identified the specific genetic characteristics that distinguish these subtypes from their respective systemic counterparts. These molecular features can improve diagnoses, determine the likelihood of concurrent or future systemic disease, and enable the rational design of novel clinical trials.

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.

A comparison of the International Consensus and 5th World Health Organization classifications of mature B-cell lymphomas

Several editions of the World Health Organization (WHO) classifications of lympho-hemopoietic neoplasms in 2001, 2008 and 2017 served as the international standard for diagnosis. Since the 4th WHO edition, here referred as WHO-HAEM4, significant clinico-pathological, immunophenotypic and molecular advances have been made in the field of lymphomas, contributing to refining diagnostic criteria of several diseases, to upgrade entities previously defined as provisional and to identify new entities. This process has resulted in two recent classifying 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, with focus on mature B-cell neoplasms. The main aim is to provide a tool to facilitate the work of pathologists, hematologists and researchers involved in the diagnosis and treatment of lymphomas.

The International Consensus Classification of Mature Lymphoid Neoplasms: a report from the Clinical Advisory Committee

Since the publication of the Revised European-American Classification of Lymphoid Neoplasms in 1994, subsequent updates of the classification of lymphoid neoplasms have been generated through iterative international efforts to achieve broad consensus among hematopathologists, geneticists, molecular scientists, and clinicians. Significant progress has recently been made in the characterization of malignancies of the immune system, with many new insights provided by genomic studies. They have led to this proposal. We have followed the same process that was successfully used for the third and fourth editions of the World Health Organization Classification of Hematologic Neoplasms. The definition, recommended studies, and criteria for the diagnosis of many entities have been extensively refined. Some categories considered provisional have now been upgraded to definite entities. Terminology for some diseases has been revised to adapt nomenclature to the current knowledge of their biology, but these modifications have been restricted to well-justified situations. Major findings from recent genomic studies have impacted the conceptual framework and diagnostic criteria for many disease entities. These changes will have an impact on optimal clinical management. The conclusions of this work are summarized in this report as the proposed International Consensus Classification of mature lymphoid, histiocytic, and dendritic cell tumors.

Update in Diagnosis and Management of Primary Cutaneous B-Cell Lymphomas

Primary cutaneous lymphomas are a rare group of diseases, with an estimated incidence of 0.5-1 case per 100,000 people per year. Primary cutaneous B-cell lymphomas (pCBCLs) represent 25-30% of all primary cutaneous lymphomas. There are three main subtypes of pCBCL: primary cutaneous marginal zone lymphoma, primary cutaneous follicle center lymphoma, and primary cutaneous diffuse large B-cell lymphoma, leg type. Cutaneous B-cell lymphomas have a broad spectrum of clinical presentations, which makes diagnostic and therapeutic strategies challenging. To date, treatment recommendations for cutaneous B-cell lymphomas have been largely based on small retrospective studies and institutional experience. Recently, the pharmacotherapeutic landscape has expanded to include drugs that may modify the underlying disease pathology of pCBCLs, representing new therapeutic modalities for this rare group of diseases. Novel therapies used for other systemic B-cell lymphomas show promise for the treatment of pCBCLs and are being increasingly considered. These new therapies are divided into five main groups: monoclonal antibodies, immune checkpoint inhibitors, small-molecule inhibitors, bispecific T-cell engaging, and chimeric antigen receptor T cell. In this review, we discuss the clinical, histopathological, molecular, and cytogenetic features of the most common pCBCL subtypes with a focus on current and innovative therapeutic developments in their management. These emerging treatment strategies for B-cell lymphomas and cutaneous B-cell lymphomas may represent novel first-line options for the management of these rare diseases.

Clinicopathologic Characteristics Associated with Prognosis in Ocular Extranodal Marginal Zone B Cell Lymphoma

Background and Objectives: Extranodal marginal zone lymphoma of the mucosa-associated lymphoid tissue (MALT) type is the most common subtype of the ocular adnexal lymphoma. Despite its excellent prognosis, some patients experience partial remission or progressive disease. We aimed to evaluate clinicopathologic differences in the treatment responder group by comparing complete remission (CR) and non-complete remission (non-CR). Materials and Methods: This study retrospectively reviewed 48 patients who were diagnosed with ocular adnexal MALT lymphoma at Ulsan University Hospital between March 2002 and August 2018. Patients who were followed up for less than 6 months were excluded. Histologic and clinical features were analyzed. The patients were divided into two groups: CR and non-CR. Results: Among the 48 patients, 33 achieved CR and 15 achieved non-CR during the median follow-up period of 40.00 months (range, 7-109 months). In univariable analysis, more patients tend to undergo treatment in the CR group, and post-radiotherapy (post-RT) SUVmax, PET and serum lactate dehydrogenase (LDH) levels were higher in the non-CR group (p = 0.043, p = 0.016, and p = 0.042, respectively). In a multivariable analysis, only application of treatment, including radiotherapy or chemotherapy with immunotherapy, was related to CR (odd ratio 7.301, 95% confidence interval 1.273-41.862, p = 0.026). In subgroup analysis according to the site of involvement, none of the variables were significant except for the post-RT SUVmax of PET and level of serum LDH in the non-conjunctiva group (p = 0.026, and p = 0.037, respectively). Seven (14.6%) patients had a recurrence, and those with a recurring site other than the primary site had a higher Ki-67 labeling index, although it was not statistically significant (9.56% vs. 18.00%, p = 0.095). Conclusions: Although belonging to the early stages, the non-CR rate was high in patients with high serum LDH levels, and recurred patients had higher Ki-67. Thus, considering active treatment is recommended in this group of patients.

Deep Sequencing of Immunoglobulin Genes Identifies a Very Low Percentage of Monoclonal B Cells in Primary Cutaneous Marginal Zone Lymphomas with CD30-Positive Hodgkin/Reed–Sternberg-like Cells

The spectrum of cutaneous CD30-positive lymphoproliferative disorders encompasses both inflammatory and neoplastic conditions. CD30+ Hodgkin and Reed–Sternberg-like cells have been occasionally reported in primary cutaneous marginal zone lymphoma, where they are thought to represent a side neoplastic component within a dominant background of lymphomatous small B cells. Herein, we describe the histological and molecular findings of three cases of primary cutaneous marginal zone lymphomas with CD30+ H/RS cells, in which next-generation sequencing analysis revealed the clonal population to consist in less than 5% of the cutaneous B-cell infiltrate, providing a thought-provoking focus on a possible main role for CD30+ cells in primary cutaneous marginal zone lymphoproliferations.

CUTANEOUS B-CELL LYMPHOMAS: UPDATE ON DIAGNOSIS, RISK-STRATIFICATION, AND MANAGEMENT

PCBCLs are a group of Non-Hodgkin's B-cell lymphomas originating in and usually confined to the skin, representing approximately one fourth of primary cutaneous lymphomas (PCL). Their current classification system has been the result of the joint World Health Organization (WHO) - European Organization for Research and Treatment of Cancer (EORTC) consensus in 2018. To date, several types of PCBCLs have been described in the scientific literature, with different clinical presentation and prognosis. Primary cutaneous follicle-center lymphoma (PCFCL) and primary cutaneous marginal zone lymphoma (PCMZL) are the most common forms, with a typical indolent course. On the contrary, primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL, LT) is less common, yet more aggressive, with a reported 5-year overall survival of approximatively 50%. In this review, we outline the PCBCLs defining diagnostic criteria, report the features of the less common subtypes and summarize the noteworthy therapeutical options currently available in this field.

IRTA1 positivity helps identify a MALT-lymphoma-like subset of primary cutaneous marginal zone lymphomas, largely but not exclusively defined by IgM expression

BACKGROUND

It has been proposed that primary cutaneous marginal zone lymphomas (PCMZLs) include a MALT-lymphoma-like IgM+ subset and a class-switched subset, which is unlike most other MALT lymphomas. Whether expression of the MALT lymphoma-associated biomarkers IRTA1 and MNDA would support this concept and whether they might help explain why some patients have both subtypes is uncertain.

METHODS

Twenty-five PCMZLs from 21 patients were stained for IRTA1 by in situ hybridization and for MNDA by immunohistochemistry. In two patients, polymerase chain reaction (PCR)-based B-cell clonality studies were performed on biopsy specimens of metachronous lesions, which expressed different heavy chains. All results were correlated with the histopathologic and clinical findings.

RESULTS

Five of six IgM+ PCMZLs were IRTA1+ vs three of 18 evaluable class-switched cases (P = 0.0069). Two of the class-switched IRTA1+ cases were in patients with clonally-related IRTA1+ IgM+ PCMZLs. IRTA1 positivity showed a statistically significant correlation with several MALT-lymphoma-associated histopathologic findings. In contrast, all PCMZL cases showed at least some MNDA expression with no differences between IgM+ and class-switched cases.

CONCLUSIONS

IRTA1 identifies MALT-lymphoma-like PCMZLs that are largely but not exclusively IgM+. This supports the concept of two PCMZL subsets but suggests their distinction should not be based solely on their heavy chain expression.

Non-scarring patchy alopecia: What else, apart from alopecia areata?

A 67-year-old woman presented with a 3-month history of patchy alopecia areata (AA)-like hair loss and multiple painful enlarged lymph nodes at cervical, nuchal, and left axillary site. The patient was on follow-up for IgM monoclonal gammopathy of undetermined significance, stable for many years. A punch biopsy from a patch of the temporal scalp revealed the presence of B-cell lymphoid infiltrates consistent with marginal zone B-cell lymphoma (MZL). Other staging examinations were conducted to make a definitive diagnosis of nodal MZL with secondary cutaneous involvement. The patient showed a complete remission of the alopecia, without evidence of scarring, after immunochemotherapy for lymphoma.

Lymphoma Classification

Twenty-five years after the Revised European American Classification of Lymphoid Neoplasms classification was published, its principle of an integrative approach to disease definition based on several parameters still prevails and has been adopted and expanded in the following World Health Organization classifications of tumors of the hematopoietic organs. The latest World Health Organization classification revised in 2017 comprises more than 80 entities of mature lymphoid neoplasms (B-cell, T-cell, and Hodgkin lymphomas), which are defined according to their morphology, immunophenotype, genetic lesions and molecular profiles, clinical features, and cellular derivation. The classification also recognizes both incipient and indolent lymphoid neoplasms with a low potential of progression. In this review, we highlight some of the new data and recent modifications introduced in the 2017 classification.

Outlines of the Japanese guidelines for the management of primary cutaneous lymphomas 2020

Since the publication of the Japanese "Guidelines for the management of cutaneous lymphomas" in 2011, the World Health Organization (WHO) classification of hematolymphoid neoplasms and the WHO-European Organisation for Research and Treatment of Cancer classification for primary cutaneous lymphomas were updated and a number of novel systemic drugs for cutaneous T-cell lymphoma had been approved in Japan. In 2020, we revised the Japanese guidelines for the management of cutaneous lymphomas with consideration of the recent advances in the understanding of the pathophysiology and classification of cutaneous lymphomas together with the update of treatment strategies reflecting the advent of novel drugs. In addition to a brief explanation of epidemiology, diagnosis, staging system, prognosis and management of each subtype of cutaneous lymphomas, the recommendations for nine clinical questions regarding treatment options that can vary even among experts are also described. A systematic review process and determination of recommendations in answer to each clinical question have been performed in accordance with the Grading of Recommendations, Assessment, Development and Evaluation scheme by a multidisciplinary expert panel consisting of dermatologists, a hematologist and a radiation oncologist. In this article, we present the outlines of the revised Japanese "Guidelines for the management of cutaneous lymphomas".

Cutaneous B-cell lymphomas: 2021 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Approximately one-fourth of primary cutaneous lymphomas are B-cell derived and are generally classified into three distinct subgroups: primary cutaneous follicle center lymphoma (PCFCL), primary cutaneous marginal zone lymphoma (PCMZL), and primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL, LT).

DIAGNOSIS

Diagnosis and disease classification is based on histopathologic review and immunohistochemical staining of an appropriate skin biopsy. Pathologic review and an appropriate staging evaluation are necessary to distinguish primary cutaneous B-cell lymphomas from systemic B-cell lymphomas with secondary skin involvement.

RISK-STRATIFICATION

Disease histopathology remains the most important prognostic determinant in primary cutaneous B-cell lymphomas. Both PCFCL and PCMZL are indolent lymphomas that infrequently disseminate to extracutaneous sites and are associated with 5-year survival rates that exceed 95%. In contrast, PCDLBCL, LT is an aggressive lymphoma with an inferior prognosis.

RISK-ADAPTED THERAPY

Both PCFCL and PCMZL patients with solitary or relatively few skin lesions may be effectively managed with local radiation therapy. While single-agent rituximab may be employed for patients with more widespread skin involvement, multi-agent chemotherapy is rarely appropriate. In contrast, management of patients with PCDLBCL, LT is comparable to the management of patients with systemic DLBCL.

How I Diagnose Primary Cutaneous Marginal Zone Lymphoma

OBJECTIVES

Primary cutaneous marginal zone lymphoma (PCMZL) is 1 of the 3 major subtypes of primary cutaneous B-cell lymphoma. The diagnosis of PCMZL may be challenging, as the differential diagnosis includes benign cutaneous lymphoproliferations as well as other primary or secondary cutaneous B-cell or T-cell lymphomas. This review describes our approach to the diagnosis of PCMZL.

METHODS

Two cases are presented that illustrate how we diagnose each of the 2 subtypes of PCMZL. The clinicopathologic features of PCMZL and the ways in which these cases can be distinguished from both benign and other neoplastic entities are emphasized.

RESULTS

A definitive diagnosis of PCMZL requires the incorporation of histologic and immunophenotypic features, molecular genetic studies in some cases, and just as importantly, clinical findings. Emerging data suggest that the heavy chain class-switched cases may be more like a clonal chronic lymphoproliferative disorder.

CONCLUSIONS

The 2 subtypes of PCMZL create different diagnostic challenges and require the use of a multiparameter approach. Although very indolent, it is important to distinguish PCMZLs from reactive proliferations, because they frequently recur and may require antineoplastic therapies. It is also critical to distinguish PCMZLs from other B- or T-cell lymphomas so that patients are properly evaluated and not overtreated.

Diagnosis and Treatment of Primary Cutaneous B-Cell Lymphomas: State of the Art and Perspectives

Primary cutaneous B-cell lymphomas are rare entities that develop primarily in the skin. They constitute a heterogeneous group that represents around a quarter of primary cutaneous lymphomas. The 2018 update of the World Health Organization-European Organization for Research and Treatment of Cancer (WHO-EORTC) classification differentiates primary cutaneous marginal zone lymphoma and primary cutaneous follicle center lymphoma with an indolent course from primary cutaneous diffuse large B-cell lymphoma, leg type with an aggressive behavior. The broad spectrum of clinical presentations and the disease course marked by frequent relapses are diagnostic and therapeutic challenges. The classification of these diseases has been refined in recent years, which allows to better define their immunopathogenesis and specific management. In the present article, we review the main clinico-biological characteristics and the current therapeutic options of these three main subsets. Based on the recent therapeutic advances in nodal B-cell lymphomas, we focus on the development of novel treatment options applicable to primary cutaneous B-cell lymphomas, including targeted therapies, combination treatments and immunotherapeutic approaches, and cover basic, translational and clinical aspects aiming to improve the treatment of cutaneous B-cell lymphomas.

Navigating the cutaneous B-cell lymphomas: avoiding the rocky shoals

In recent years great progress has been made in understanding the classification of lymphomas. The integration of morphologic, clinical, immunophenotypic, and molecular features provides a rational basis for defining disease entities and has led to worldwide consensus. Hematopathologists and dermatopathologists have worked together to define those lymphomas that are present most commonly in the skin. Some cutaneous lymphomas have distinctive features and differ from their nodal counterparts. This is most evident in the delineation of primary cutaneous follicle center lymphoma and primary cutaneous marginal zone lymphoma. Both are very indolent, with low risk to spread beyond the skin. Primary cutaneous marginal zone lymphoma shows evidence of immunoglobulin class switching, as distinct from involvement by other extranodal marginal zone lymphomas of MALT type, which may involve the skin secondarily. Some have suggested that primary cutaneous marginal zone lymphoma may be considered a benign clonal expansion, probably driven by antigen. Many cutaneous lymphomas share biological and clinical features with their systemic counterparts. For example, primary cutaneous large B-cell lymphoma, leg type, exhibits a similar gene expression and molecular profile as diffuse large B-cell lymphoma of the activated B-cell type, especially for those cases arising in other extranodal sites. In addition, Epstein-Barr virus plays a role in many cutaneous lesions including mucocutaneous ulcer, plasmablastic lymphoma, and even some cases of marginal zone lymphoma. These EBV-driven conditions may present primarily in the skin, but also involve other mainly extranodal sites. Thus, it is evident that some cutaneous and systemic lymphomas are driven by common pathogenetic mechanisms, necessitating an integrated approach for the classification of lymphoma in all sites.

AL-Amyloidoma of the Skin-A Rare Manifestation of Primary Cutaneous Marginal Zone Lymphoma

AL-amyloidoma is considered to be a variant of primary cutaneous marginal zone lymphoma (pcMZL). A 51-year-old white man presented a 2 × 2-cm erythematous to brownish waxy plaque on the back of the scalp. The plaque was first noticed 16 years ago. It was asymptomatic, and the patient was otherwise healthy. The lesion was excised. Histological examination revealed dermal deposits of amyloid and a subtle perivascular infiltrate, predominately consisting of plasma cells. Infiltrating cells expressed CD79a, bcl2, and IgG and were negative for bcl6, CD56, and IgM. A monoclonal light-chain expression of lambda (lambda:kappa = 10:1) was demonstrated by in situ hybridization. The diagnosis of pcMZL, presenting as an AL-amyloidoma, was made because staging procedures excluded systemic manifestation of lymphoma, monoclonal gammopathy, and systemic amyloidosis. Cutaneous amyloid deposits with monoclonal plasma cell proliferation can occur as a result of monoclonal gammopathy/plasmocytoma or as a rare manifestation of pcMZL. Systemic B-cell lymphoma and systemic monoclonal plasma cell proliferations have to be excluded.

Marginal zone B-cell lymphoma: lessons from Western and Eastern diagnostic approaches

Marginal zone B-cell lymphomas (MZLs) are a group of clinically indolent B-cell lymphomas postulated to derive from memory B lymphocytes in the 'marginal zone' of secondary lymphoid tissue. Today, MZL is recognised as a nosological umbrella term encompassing distinct entities with some shared phenotypic and genotypic features, including extranodal marginal zone B-cell lymphoma (EMZL) or mucosa-associated lymphoid tissue (MALT) lymphoma, splenic MZL, and nodal MZL, accounting for approximately 70%, 20%, and 10% of MZLs, respectively. These lymphomas share some phenotypic and genotypic features and have some variants and related provisional diseases, but are different in regards to their clinical and molecular characteristics. In addition, they are frequently associated with chronic antigenic stimulation represented either by infectious agents, particularly bacteria and viruses, or autoimmune diseases as exemplified by Sjögren syndrome, Hashimoto thyroiditis, and newly recognised IgG4-related disease. Furthermore, several chromosomal translocations have been identified in EMZL. In this review, we will focus on the updated histopathological criteria and the main problems with differential diagnoses in order to aid the diagnostic approach in our routine practice.

Prevalence of atopy and staphylococcal superantigen-specific immunoglobulin E (IgE) antibodies and total serum IgE in primary cutaneous T- and B-cell lymphoma

The prevalence of atopy was investigated in 20 patients with Sézary syndrome (SS), 20 patients with plaque phase mycosis fungoides (MF), 9 patients with primary cutaneous marginal zone lymphoma (pcMZL) and 8 patients with primary cutaneous follicle center lymphoma (pcFCL) with the Phadiatop multi-allergen test. The relationship among serologic atopy, IgE reactivity against Staphyloccocal enterotoxin superantigens, and serum total IgE (IgE-t) levels and their prognostic implications in SS was investigated. Phadiatop test was positive in 45%, 15%, 33% and 0% of samples of SS, MF, pcMZL and pcFCL, respectively. IgE-t levels were also increased in SS, pcMZL and marginally MF. No correlation was found with patients' history of atopic disorders. Staphylococcal superantigen-specific IgE ≥ 0.35 kUa/L, most often against toxic shock syndrome toxin-1, was detected in 40% of Sézary samples followed by MF (20%). In the absence of serologic atopy (negative Phadiatop test), IgE-t levels for patients with SS and MF were not significantly higher than controls whereas the levels for pcMZL remained high. Furthermore, even with a negative Phadiatop test, IgE-t values were higher in sera of patients with SSAg-IgE ≥ 0.35 kUa/L vis-à-vis < 0.35 kUa/L across all diagnostic categories including controls albeit the difference was statistically significant only for SS. The presence of specific IgE antibodies ≥ 0.35 kUa/L, IgE-t > 122 kU/L or eosinophils > 500/µL had no impact on survival of patients with SS. These results indicate that a pathogenic link may exist between an atopic diathesis and development of SS and possibly pcMZL.

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.

Indolent T-cell-rich small B-cell hepatic lymphoma in a Golden Retriever

An 11-year-old female spayed Golden Retriever presented for an incidentally found liver mass. The hepatic mass and intra-abdominal lymph nodes had a marked heterogeneous T-cell population and far fewer numbers of small clonal B cells. This T-cell-rich small B-cell lymphoma had a unique histological pattern and indolent clinical course.

Primary Cutaneous B-cell Lymphomas

B-cell lymphomas represent approximately 20% to 25% of primary cutaneous lymphomas. Within this group, most cases (>99%) are encompassed by 3 diagnostic entities: primary cutaneous marginal zone lymphoma, primary cutaneous follicle center lymphoma, and primary cutaneous diffuse large B-cell lymphoma, leg type. In this article, the authors present clinical, histopathologic, immunophenotypic, and molecular features of each of these entities and briefly discuss the rarer intravascular large B-cell lymphoma.

Primary cutaneous B-cell lymphoma: narrative review of the literature

Primary cutaneous B-cell lymphomas comprehend a group of lymphoproliferative disorders characterized by being monoclonal proliferations of B-cell primarily involving the skin. Despite being recognized as autonomous and distinct clinico-pathologic entities since the late 80s, their classification is still an ongoing matter of debate. At the moment, WHO classification recognizes three disorders: primary cutaneous marginal zone lymphoma, primary cutaneous follicle center lymphoma and primary cutaneous diffuse large b-cell lymphoma (leg type). Primary cutaneous diffuse large b-cell lymphoma (other) has been used to define rare cases which show histologically an infiltrate with diffuse pattern composed by large b-cell, but not fitting with criteria for follicle center lymphoma nor for primary cutaneous diffuse large b-cell lymphoma (leg type). Aim of this review was to briefly describe all recognized and provisional entities included in the primary cutaneous b-cell lymphomas and to discuss recent acquisitions that may influence their future classifications.

Frequent immunoglobulin G4 expression in a common variant of primary cutaneous marginal zone B-cell lymphoma

Immunoglobulin (Ig)G4 expression was recently observed in a proportion of primary cutaneous marginal zone B-cell lymphoma (PCMZL) with plasmacytic differentiation. IgG4-related disease is characterised by polyclonal lymphoplasmacytic infiltration with IgG4 expression, storiform fibrosis and obliterative phlebitis in histopathology. Here we report three cases of common variants of PCMZL with predominant and varied IgG4 expression, suggesting there is an underlying clonal progression between these two entities.

The role of G protein-coupled receptors in lymphoid malignancies

B cell lymphoma consists of multiple individual diseases arising throughout the lifespan of B cell development. From pro-B cells in the bone marrow, through circulating mature memory B cells, each stage of B cell development is prone to oncogenic mutation and transformation, which can lead to a corresponding lymphoma. Therapies designed against individual types of lymphoma often target features that differ between malignant cells and the corresponding normal cells from which they arise. These genetic changes between tumor and normal cells can include oncogene activation, tumor suppressor gene repression and modified cell surface receptor expression. G protein-coupled receptors (GPCRs) are an important class of cell surface receptors that represent an ideal target for lymphoma therapeutics. GPCRs bind a wide range of ligands to relay extracellular signals through G protein-mediated signaling cascades. Each lymphoma subgroup expresses a unique pattern of GPCRs and efforts are underway to fully characterize these patterns at the genetic level. Aberrations such as overexpression, deletion and mutation of GPCRs have been characterized as having causative roles in lymphoma and such studies describing GPCRs in B cell lymphomas are summarized here.

A Literature Revision in Primary Cutaneous B-cell Lymphoma

The term “Primary Cutaneous B-Cell Lymphoma” (PCBCL) comprehends a variety of lymphoproliferative disorders characterized by a clonal proliferation of B-cells primarily involving the skin. The absence of evident extra-cutaneous disease must be confirmed after six-month follow-up in order to exclude a nodal non-Hodgkin's lymphoma (NHL) with secondary cutaneous involvement, which may have a completely different clinical behavior and prognosis. In this article, we have summarized the clinico-pathological features of main types of PCBCL and we outline the guidelines for management based on a review of the available literature.

Cutaneous marginal zone lymphomas

Primary cutaneous marginal zone lymphoma (CMZL) is one of the major primary B-cell lymphomas of skin. Two types are recognized: a more common class-chain switched CMZL, and a much less common IgM+ CMZL. The extremely indolent course, together with other features distinct from most other MALT lymphomas, has led some to question whether at least the class-switched cases should be considered an overt lymphoma.

A subset of ocular adnexal marginal zone lymphomas may arise in association with IgG4-related disease

We previously suggested a relationship between ocular immunoglobulin (Ig)G4-related disease (IgG4-RD) and marginal zone lymphomas (MZLs). However, the cytokine background associated with these disorders and whether it differs between ocular adnexal MZLs with (IgG4-associated MZL) and without (IgG4-negative MZL) numerous IgG4⁺ plasma cells are unknown. In this study, we identified the mRNA expression pattern of Th2 and regulatory T-cell (Treg) cytokines in IgG4-RD and in IgG4-associated MZL and IgG4-negative MZL using real-time polymerase chain reaction analysis. Ocular IgG4-RD and IgG4-associated MZL exhibited significantly higher expression ratios of interleukin (IL)-4/β-actin, IL-10/β-actin, IL-13/β-actin, transforming growth factor (TGF) β1/β-actin, and FOXP3/β-actin than did IgG4-negative MZL (p < 0.05). This finding further supports our prior observations that a significant subset of ocular MZLs arises in the setting of IgG4-RD. Furthermore, the presence of a different inflammatory background in IgG4-negative MZLs suggests that IgG4-associated MZLs may have a different pathogenesis.

Evaluating breast lymphoplasmacytic infiltrates: a multiparameter immunohistochemical study, including assessment of IgG4

Lymphoplasmacytic infiltrates in the breast, a modified skin appendage, include lymphocytic lobulitis, other nonspecific benign proliferations, and mucosa-associated lymphoid tissue (MALT)-type lymphoma. Distinguishing these entities, all of which may be B-cell rich and may have associated sclerosis, can be difficult. In addition, the proportion that represents IgG4-related disease is unknown, and the similarity of MALT lymphomas to primary cutaneous marginal zone lymphoma is uncertain. To address these questions, the clinical, histologic, and immunohistochemical features of 50 benign and malignant breast lymphoplasmacytic infiltrates (10 lymphocytic lobulitis, 1 granulomatous, 19 not otherwise specified, 20 MALT lymphomas) were evaluated. Compared with the MALT lymphomas, benign cases had a less dense infiltrate (P < .001), fewer but more histologically apparent germinal centers (P < .001), and more marked fibrosis (P < .0001). Greater than 60% B cells were present in 23% (7/30) benign cases versus 75% (15/20) MALT lymphomas (P = .0003). Plasma cells were predominantly IgG+ in 83% (24/29) benign cases and predominantly IgM+ in 73% (14/19) MALT lymphomas (P < .0001). None of the benign cases had greater than 50 IgG4+ plasma cells/high-power field, and only 1 lymphocytic lobulitis case had an IgG4/IgG ratio exceeding 40% and no clinical evidence for extramammary IgG4-related disease. Although there may be some overlapping features, routine histopathology together with limited immunohistochemical stains can distinguish benign from neoplastic lymphoplasmacytic infiltrates in the breast. Despite frequent sclerosis, the breast is not a common site of unrecognized IgG4-related sclerosing disease. Although there are similarities, breast MALT lymphomas can be separated from cutaneous marginal zone lymphoma.

Cutaneous lymphomas: an update. Part 2: B-cell lymphomas and related conditions

: Primary cutaneous B-cell lymphomas (PCBCL) are the second most common form of primary cutaneous lymphomas and account for approximately 25%-30% of all primary cutaneous lymphomas. Both forms of low-grade malignant PCBCL, primary cutaneous follicle center lymphoma (PCFCL) and primary cutaneous marginal zone lymphoma of mucosa-associated lymphoid tissue-type (MALT lymphoma) (PCMZL) represent the vast majority of PCBCL and show an indolent slowly progressive course and an excellent prognosis despite a high recurrence rate. Genetic analysis indicates that PCMZL differ from other forms of extranodal MALT lymphomas. The more common class-switched and the non-class-switched form of PCMZL can be distinguished as two distinctive subsets that differ in the cellular composition, IgM expression, and biological behavior with extracutaneous involvement found in the non-class-switched form. Recently, unusual clinical and histological forms of PCMZL and PCFCL manifesting with miliary or agminated lesions have been described that are diagnostically challenging. In contrast to PCMZL and PCFCL, primary cutaneous diffuse large B-cell lymphoma, leg type, and other rare forms of large B-cell lymphomas such as intravascular large B-cell lymphoma have an unfavorable prognosis. There is an emerging group of Epstein-Barr virus (EBV)-driven B-cell lymphoproliferations including posttransplant lymphoproliferative disorders and mucocutaneous ulcer occurring in immunocompromised patients and EBV-associated diffuse large B-cell lymphoma of the elderly arising in the setting of senescence-linked immunodeficiency. This review reports on recent findings expanding the spectrum of clinicopathological features, differential diagnostic aspects, and the pathogenesis of PCBCL and discusses the group of EBV-associated B-cell lymphoproliferations involving the skin.

Recent advances in primary cutaneous B-cell lymphomas

PURPOSE OF REVIEW

In the last decade, there has been considerable debate regarding the classification and terminology of the group of primary cutaneous B-cell lymphomas (CBCLs). With the introduction of the WHO-EORTC classification for cutaneous lymphomas, three main types of CBCLs are recognized: primary cutaneous marginal zone B-cell lymphoma (PCMZL), primary cutaneous follicle centre lymphoma (PCFCL) and primary cutaneous large B-cell lymphoma, leg type (PCLBCL, LT).

RECENT FINDINGS

Epidemiological studies performed on different patient cohorts showed that the CBCL entities described in the WHO-EORTC classification and the 4th WHO classification of tumours of haematopoietic and lymphoid tissues are reproducible worldwide and are clinically relevant, thereby illustrating the clinical usefulness of the WHO-EORTC classification. Furthermore, collaborative studies between the ISCL and EORTC lymphoma group resulted in recommended staging procedures and consensus treatment recommendations for different CBCL subtypes.

SUMMARY

The advances in the classification, staging procedures and treatment of CBCLs have led to a major improvement in clinical care. The progress in CBCL classification enables molecular studies on well defined groups of patients and facilitates comparison of treatment results between different centres. Recent studies found that intralesional/intravenous rituximab has a therapeutic value in PCFCL and PCMZL with widespread cutaneous lesions and suggest that therapies targeting the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) pathway could be helpful in DLBCL, LT.

Primary cutaneous marginal zone lymphomas with plasmacytic differentiation show frequent IgG4 expression

The expression of IgG4 in malignant B-cell lymphomas has only partially been studied. Recent reports described single cases of marginal zone lymphomas arising in the ocular adnexae that express IgG4. Moreover, a subset of dura-associated marginal zone lymphomas appear to express IgG4 as well. We investigated IgG4 expression in a more systematic manner in a large cohort of marginal zone lymphoma specimens derived from the archive of our institute. Overall, we examined 169 marginal zone lymphomas of various primary sites that displayed a distinct plasmacytic differentiation and light chain restriction, allowing for a detailed investigation of the immunoglobulin heavy chain expression in these tumors by immunohistochemistry. Unexpectedly, primary cutaneous marginal zone lymphomas showed frequent IgG4 expression. Although only 1 out of 120 noncutaneous marginal zone lymphomas, located in the ocular adnexae, expressed IgG4, 19 of 49 (39%) primary cutaneous marginal zone lymphomas showed this feature, constituting the highest expression rate of IgG4 reported to date in any B-cell lymphoma. None of the IgG4-positive cutaneous marginal zone lymphomas with available clinical data showed evidence of a preexisting systemic IgG4-related disease, suggesting a localized immunologic IgG4-driven pathogenetic process at early stages of the disease. IgG4-positive and IgG4-negative primary cutaneous marginal zone lymphomas did not significantly differ in architectural features of the infiltrate or the composition of the reactive T-cell infiltrate as determined by analysis of T-cell content, CD4/CD8 ratio, and content of FOXP3- and PD1-positive T cells. Although the pathogenetic role of IgG4 expression in a significant subset of primary cutaneous marginal zone lymphomas with plasmacytic differentiation remains unclear at present, the demonstration of IgG4 expression in a marginal zone lymphoma involving the skin might be a helpful clue in the routine diagnostic setting, as these tumors will almost invariably be of primary cutaneous origin with an extremely low risk of spread to noncutaneous sites and an excellent prognosis.

Marginal zone lymphomas and infectious agents

A link with infectious agents, bacteria and viruses in particular, has been reported for many lymphoma entities. Marginal zone lymphomas (extranodal, nodal and splenic forms) are frequently associated with chronic infections, with important clinical, molecular, biological, and therapeutic implications. The well-known correlation between Helicobacter pylori and gastric MALT-lymphoma, the recently reported links between Chlamydophila psittaci and ocular adnexal MALT-lymphoma and Borrelia burgdorferi and cutaneous MALT lymphoma constitute the best studied examples of lymphomagenic activity of bacteria, while the hepatitis C virus represents the most extensively investigated virus associated with marginal zone lymphomas. Biological and clinical features, therapeutic implications and future perspectives of these lymphoma-microbial associations are discussed in this review.