High Incidence and Clinical Significance of MYC Rearrangements in Primary Cutaneous Diffuse Large B-Cell Lymphoma, Leg Type

Cutaneous B-Cell Lymphomas

Primary cutaneous B-cell lymphomas represent a type of non-Hodgkin's lymphoma of the skin without evidence of extracutaneous involvement at the time of diagnosis. According to the 2018 World Health Organization-the European Organization for Research and Treatment of Cancer classification, primary cutaneous B-cell lymphomas include primary cutaneous marginal zone lymphoma, primary cutaneous follicle center lymphoma, primary cutaneous diffuse large B-cell lymphoma, leg type, intravascular large B-cell lymphoma, and Epstein-Barr virus+ mucocutaneous ulcer (provisional). Herein, we provide a comprehensive review of the updated literature on these entities, including clinical presentation, histopathology, immunophenotype, molecular genetics, prognosis, and treatment.

Sinonasal DLBCL: molecular profiling identifies subtypes with distinctive prognosis and targetable genetic features

ABSTRACT

Primary sinonasal diffuse large B-cell lymphoma (PSDLBCL) is a rare lymphoma with a variable prognosis and a unique relapse/dissemination pattern involving the central nervous system and skin. The underlying molecular mechanisms leading to this heterogeneity and progression pattern remain uncharted, hampering patient-tailored treatment. To investigate associated mechanisms, we analyzed clinical data and used immunohistochemistry, gene-expression profiling, cytogenetics, and next-generation sequencing in a cohort of 117 patients with PSDLBCL. The distribution in cell-of-origin (COO) was 68 (58%) activated B-cell (ABC), 44 (38%) germinal center B-cell (GCB), and 5 (4%) unclassifiable. COO was significantly associated with progression-free survival (PFS) and lymphoma-specific mortality (LSM) in both the overall cohort (5-year PFS: ABC, 43% vs GCB, 73%; LSM: ABC, 45% vs GCB, 14%) and in the subgroup of patients receiving immunochemotherapy (5-year PFS: ABC, 55% vs GCB, 85%; LSM: ABC, 28% vs GCB, 0%). ABC lymphomas were mainly MCD class, showing a high prevalence of MYD88 (74%) and CD79B (35%) mutations compared with GCB lymphomas (MYD88 23%; CD79B 10%) (P < .01). The ABC subtype frequently displayed cMYC/BCL2 coexpression (76% vs 18% GCB; P < .001) and HLA-II loss (48% vs 10% GCB; P < .001). PD-L1 expression and copy-number alterations were rare. All lymphomas were Epstein-Barr virus-negative. Our data suggest molecular profiling as a potent tool for detecting prognostic subgroups in PSDLBCL, exposing links to known relapse/dissemination sites. The ABC subgroup's MCD genetic features, shared with lymphomas at other nonprofessional lymphoid sites, make them potential candidates for targeted B-cell and toll-like receptor signaling therapy.

Predictive and prognostic molecular biomarkers in lymphomas

Recent advances in molecular diagnostics have markedly expanded our understanding of the genetic underpinnings of lymphomas and catalysed a transformation in not just how we classify lymphomas, but also how we treat, target, and monitor affected patients. Reflecting these advances, the World Health Organization Classification, International Consensus Classification, and National Comprehensive Cancer Network guidelines were recently updated to better integrate these molecular insights into clinical practice. We summarise here the molecular biomarkers of lymphomas with an emphasis on biomarkers that have well-supported prognostic and predictive utility, as well as emerging biomarkers that show promise for clinical practice. These biomarkers include: (1) diagnostic entity-defining genetic abnormalities [e.g., B-cell acute lymphoblastic leukaemia (B-ALL) with KMT2A rearrangement]; (2) molecular alterations that guide patients' prognoses (e.g., TP53 loss frequently conferring worse prognosis); (3) mutations that serve as the targets of, and often a source of acquired resistance to, small molecular inhibitors (e.g., ABL1 tyrosine kinase inhibitors for B-ALL BCR::ABL1, hindered by ABL1 kinase domain resistance mutations); (4) the growing incorporation of molecular measurable residual disease (MRD) in the management of lymphoma patients (e.g., molecular complete response and sequencing MRD-negative criteria in multiple myeloma). Altogether, our review spans the spectrum of lymphoma types, from the genetically defined subclasses of precursor B-cell lymphomas to the highly heterogeneous categories of small and large cell mature B-cell lymphomas, Hodgkin lymphomas, plasma cell neoplasms, and T/NK-cell lymphomas, and provides an expansive summary of our current understanding of their molecular pathology.

Prognostic significance of copy number gains of MYC detected by fluorescence in situ hybridization in large B-cell lymphoma

The MYC protooncogene plays a critical role in many cellular processes. MYC translocations are recurrent in large B-cell lymphomas (LBCLs) where they exhibit a negative effect on survival. Gain of MYC copies is also frequently identified; however, there is no consensus on the frequency and prognostic significance of MYC copy gains. We collected FISH data for MYC with reflex testing for BCL2 and BCL6 and IHC results at diagnosis for a cohort of 396 de novo and transformed LBCL cases and compared progression-free (PFS) and overall survival (OS) to determine the prognostic impact of extra MYC copies. The prevalence of cases with MYC copy number gain was 20.9%. PFS was shorter for patients with ≥5 MYC copies compared to controls (p = 0.0005, HR = 2.25). .MYC gain trended towards worse OS; patients with ≥7MYC copies had worse OS (p = 0.013), similar to patients with MYC translocations. We propose that MYC gain represents a dose-dependent prognostic factor for LBCLs.

Artificial intelligence in digital pathology of cutaneous lymphomas: a review of the current state and future perspectives

Primary cutaneous lymphomas (CLs) represent a heterogeneous group of T-cell lymphomas and B-cell lymphomas that present in the skin without evidence of extracutaneous involvement at time of diagnosis. CLs are largely distinct from their systemic counterparts in clinical presentation, histopathology, and biological behavior and, therefore, require different therapeutic management. Additional diagnostic burden is added by the fact that several benign inflammatory dermatoses mimic CL subtypes, requiring clinicopathological correlation for definitive diagnosis. Due to the heterogeneity and rarity of CL, adjunct diagnostic tools are welcomed, especially by pathologists without expertise in this field or with limited access to a centralized specialist panel. The transition into digital pathology workflows enables artificial intelligence (AI)-based analysis of patients' whole-slide pathology images (WSIs). AI can be used to automate manual processes in histopathology but, more importantly, can be applied to complex diagnostic tasks, especially suitable for rare disease like CL. To date, AI-based applications for CL have been minimally explored in literature. However, in other skin cancers and systemic lymphomas, disciplines that are recognized here as the building blocks for CLs, several studies demonstrated promising results using AI for disease diagnosis and subclassification, cancer detection, specimen triaging, and outcome prediction. Additionally, AI allows discovery of novel biomarkers or may help to quantify established biomarkers. This review summarizes and blends applications of AI in pathology of skin cancer and lymphoma and proposes how these findings can be applied to diagnostics of CL.

Large B-Cell Lymphomas in the 5th Edition of the WHO-Classification of Haematolymphoid Neoplasms-Updated Classification and New Concepts

The family/class of the large B-cell lymphomas (LBCL) in the 5th edition of the World Health Organization (WHO) classification of haematolymphoid tumors (WHO-HAEM5) features only a few major changes as compared to the 4th edition. In most entities, there are only subtle changes, many of them only representing some minor modifications in diagnostic terms. Major changes have been made in the diffuse large B-cell lymphomas (DLBCL)/high-grade B-cell lymphomas (HGBL) associated with MYC and BCL2 and/or BCL6 rearrangements. This category now consists of MYC and BCL2 rearranged cases exclusively, while the MYC/BCL6 double hit lymphomas now constitute genetic subtypes of DLBCL, not otherwise specified (NOS) or of HGBL, NOS. Other major changes are the conceptual merger of lymphomas arising in immune-privileged sites and the description of LBCL arising in the setting of immune dysregulation/deficiency. In addition, novel findings concerning underlying biological mechanisms in the pathogenesis of the different entities are provided.

Prevalence and prognostic value of MYD88 and CD79B mutations in ocular adnexal large B-cell lymphoma: a reclassification of ocular adnexal large B-cell lymphoma

AIMS

To (1) reclassify ocular adnexal large B-cell lymphomas (OA-LBCLs) per 2016 WHO lymphoma classification and (2) determine the prevalence of MYD88 and CD79B mutations and their association with clinical parameters among OA-LBCLs.

METHODS

This study is a retrospective analysis of all OA-LBCLs diagnosed in Denmark between 1980 and 2018. Medical records and tissue samples were retrieved. Thirty-four OA-LBCLs were included. Fluorescence in situ hybridisation and Epstein-Barr-encoded RNA in situ hybridisation were used for the reclassification. Mutational status was established by allele-specific PCR and confirmed by Sanger sequencing. Primary endpoints were overall survival, disease-specific survival (DSS) and progression-free survival (PFS).

RESULTS

Two LBCL subtypes were identified: diffuse large B-cell lymphoma (DLBCL) (27 of 32; 84%) and high-grade B-cell lymphoma (HGBL) with MYC and BCL2 and/or BCL6 rearrangements (5 of 32; 16%). cMYC/BCL2 double-expressor DLBCLs had a poorer DSS than non-double-expressor DLBCLs (5-year DSS, 25% vs 78%) (HR 0.23; 95% CI 0.06 to 0.85; p=0.014). MYD88 mutations were present in 10 (29%) of 34 lymphomas and carried a poorer PFS than wild-type cases (5-year PFS, 0% vs 43%) (HR 0.78; 95% CI 0.61 to 0.98; p=0.039). CD79B mutations were present in 3 (9%) of 34 cases.

CONCLUSION

OA-LBCL consists mainly of two subtypes: DLBCL and HGBL with MYC and BCL2 and/or BCL6 rearrangements. MYD88 mutations are important drivers of OA-LBCL. MYD88 mutations, as well as cMYC/BCL2 double-expressor DLBCL, appear to be associated with a poor prognosis. Implementing MYD88 mutational analysis in routine diagnostics may improve OA-LBCL prognostication.

Primary Cutaneous B-Cell Lymphomas with Large Cell Morphology: A Practical Review

Most primary cutaneous lymphomas consist of T-cell lymphomas or small cell lymphomas; however, the skin may also be affected by lymphomas with large cell morphology, as a primary or secondary localization. A minority of cases consist of primary cutaneous B-cell lymphomas (PCBCLs). PCBCLs are a heterogeneous group of rare neoplasms with an overlapping morphological and immunohistochemical picture of the different subtypes. Nevertheless, differential diagnosis in the setting of this group of neoplasms is mandatory to identify the correct therapy and prognosis, but it may be challenging since, due to the rarity of these neoplasms, they may not always be familiar to pathologists. Indeed, immunohistochemistry may not be enough to distinguish the different histotypes, which overlap in immunohistochemical features. Furthermore, the ever-increasing knowledge of the molecular features of systemic B-cell lymphomas, such as gene rearrangements with clinical significance, has led in recent years to further investigation into the molecular landscape of PCBCLs with large cell morphology. This work aimed to provide a practical diagnostic guide for pathologists dealing with primary cutaneous large B-cell lymphomas.

Aggressive Cutaneous Lymphomas and Their Mimics

Cutaneous lymphomas encompass a heterogeneous group of neoplasms with a wide spectrum of clinical presentations, histopathologic features, and prognosis. Because there are overlapping pathologic features among indolent and aggressive forms and with systemic lymphomas that involve the skin, clinicopathologic correlation is essential. Herein, the clinical and histopathologic features of aggressive cutaneous B- and T-cell lymphomas are reviewed. Indolent cutaneous lymphomas/lymphoproliferative disorders, systemic lymphomas, and reactive processes that may mimic these entities are also discussed. This article highlights distinctive clinical and histopathologic features, increases awareness of rare entities, and presents new and evolving developments in the field.

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.

Integrative diagnosis of primary cutaneous large B-cell lymphomas supports the relevance of cell of origin profiling

Primary cutaneous large B-cell lymphomas (PCLBCL) represent a diagnostic challenge because they are classified as PCLBCL, leg type (PCLBCL, LT) or primary cutaneous follicle centre lymphoma, large cell (PCFCL, LC), which differ by prognosis and therapeutic requirement. Unclassified cases with discordant clinical presentations, morphologies, and immunophenotypes may be classified into the not otherwise specified (PCLBCL, NOS) category based on ancillary molecular analyses. Cell-of-origin profiling as germinal centre (GC) type or non-GC type by immunohistochemistry is not considered reproducible because of variable CD10 expression. In a series of 55 PCLBCL cases with > 80% large cells, we reported 21 PCFCL, LC cases as GC-type and 27 PCLBCL, LT as non-GC-type; 7 cases were considered PCLBCL, NOS. Here, we demonstrate the accuracy of molecular profiling of PCLBCL as GC or non-GC type using a reverse transcriptase multiplex ligation assay (RT-MLPA). RT-MLPA classified the seven PCLBCL, NOS cases in accordance with their mutational profile. An integrative principal component analysis confirmed the main criteria and the relevance of genomic profiling of PCFCL, LC as GC-derived, and PCLBCL, LT as non-GC-derived. Both the cell-of-origin classification of PCLBCL and the integrative analysis identified two clinically relevant subgroups according to overall survival, which may help to standardize PCLBCL diagnosis and patient management.

Prognostic value of Bcl2 and Bcl6 in primary cutaneous large B-cell lymphoma: A systematic review and meta-analysis

AIMS

To assess the prognostic value of Bcl2 and Bcl6 in primary cutaneous diffuse large B-cell lymphoma (pcDLBCL), through a systematic review and meta-analysis.

METHODS

Electronic databases were searched from their inception to April 2021 for studies reporting Bcl2 and Bcl6 expression and survival outcomes in pcDLBCL series. Kaplan-Meier and Cox regression survival analyses with hazard ratio calculation were performed for overall survival (OS), with a significant p-value< 0.05.

RESULTS

Eight studies with 148 patients were included. OS was significantly decreased in Bcl2-pos itive pcDLBCLs (5-year OS= 52.9 ± 5.2%) compared to Bcl2 negative pcDLBCLs (5-year OS= 86.6 ± 7.2%), with a HR of 4.615 (95% CI, 1.827-11.657; p = 0.001); no significant difference in OS was found between Bcl6-positive pcDLBCLs (5-year OS= 61.3 ± 6.5%) and Bcl6-negative pcDLBCLs (5-year OS= 56.8 ± 7.2%), with a HR of 0.789 (95% CI, 0.462-1.350; p = 0.388).

CONCLUSIONS

In pcDLBCL, Bcl2 expression is a strong unfavourable prognostic marker; Bcl6 does not seem to be associated with survival instead. Further studies are necessary in this field.

Cell-of-origin classification using the Hans and Lymph2Cx algorithms in primary cutaneous large B-cell lymphomas

Primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL-LT) and primary cutaneous follicle center lymphoma with a diffuse population of large cells (PCFCL-LC) are both primary cutaneous B-cell lymphomas with large-cell morphology (CLBCL) but with different clinical characteristics and behavior. In systemic diffuse large B-cell lymphoma, not otherwise specified (DLBCL-NOS), gene-expression profiling (GEP) revealed two molecular subgroups based on their cell-of-origin (COO) with prognostic significance: the germinal center B-cell-like (GCB) subtype and the activated B-cell-like (ABC) subtype. This study investigated whether COO classification is a useful tool for classification of CLBCL. For this retrospective study, 51 patients with PCDLBCL-LT and 15 patients with PCFCL-LC were analyzed for their COO according to the immunohistochemistry-based Hans algorithm and the NanoString GEP-based Lymph2Cx algorithm. In PCFCL-LC, all cases (100%) classified as GCB by both Hans and Lymph2Cx. In contrast, COO classification in PCDLBCL-LT was heterogeneous. Using Hans, 75% of the PCDLBCL-LT patients classified as non-GCB and 25% as GCB, while Lymph2Cx classified only 18% as ABC, 43% as unclassified/intermediate, and 39% as GCB. These COO subgroups did not differ in the expression of BCL2 and IgM, mutations in MYD88 and/or CD79B, loss of CDKN2A, or survival. In conclusion, PCFCL-LC uniformly classified as GCB, while PCDLBCL-LT classified along the COO spectrum of DLBCL-NOS using the Hans and Lymph2Cx algorithms. In contrast to DLBCL-NOS, the clinical relevance of COO classification in CLBCL using these algorithms has limitations and cannot be used as an alternative for the current multiparameter approach in differentiation of PCDLBCL-LT and PCFCL-LC.

Diagnosis and prognostic stratification of cutaneous lymphoma

Primary cutaneous lymphomas are a heterogenous group of non-Hodgkin's lymphoma of both T/natural killer-cell and B-cell origin and defined to primarily present in the skin without extracutaneous involvement at diagnosis. In contrast to nodal non-Hodgkin's lymphoma, cutaneous T-cell lymphomas (CTCL) are more generally seen than cutaneous B-cell lymphomas (CBCL). CTCL and CBCL have various subtypes and each subtype has specifically characteristic clinical, pathological, and prognostic features. The diagnostic methods and staging evaluation of cutaneous lymphomas is mostly common in various guidelines created by professional societies. The diagnosis is made comprehensively based on clinical, pathological, laboratory, radiological, and genetic findings. On the other hand, definite prognostic stratification has not been completely established yet in most cutaneous lymphomas. This article focuses on the general and novel diagnostic methods and the current findings about prognostic factors and stratification in cutaneous lymphomas.

Molecular Update and Evolving Classification of Large B-Cell Lymphoma

Diffuse large B-cell lymphomas (DLBCLs) are aggressive B-cell neoplasms with considerable clinical, biologic, and pathologic diversity. The application of high throughput technologies to the study of lymphomas has yielded abundant molecular data leading to the identification of distinct molecular identities and novel pathogenetic pathways. In light of this new information, newly refined diagnostic criteria have been established in the fourth edition of the World Health Organization (WHO) consensus classification of lymphomas, which was revised in 2016. This article reviews the histopathological and molecular features of the various aggressive B-cell lymphoma subtypes included in the updated classification.

Double expressor and double/triple hit status among primary cutaneous diffuse large B-cell lymphoma: a comparison between leg type and not otherwise specified subtypes

Primary cutaneous diffuse large B-cell lymphomas (pcDLBCLs) are rare hematological neoplasms. The pcDLBCL category includes primary cutaneous large B-cell lymphoma leg type (pcDLBCL-LT), characterized by a particularly unfavorable outcome, and primary cutaneous large B-cell lymphoma not otherwise specified (pcDLBCL-NOS), a widely debated subentity with a more indolent course. The negative prognostic impact of double expressor status (DE status, given by coexpression of MYC and BCL2) and double hit/triple hit status (DH/TH status, given by translocations of MYC and BCL2 and/or BCL6) in nodal DLBCL is well known; however, no unanimous conclusions regarding relevance of DE and DH/TH status have been reached in pcDLBCL. Therefore, our purpose has been to investigate the presence and prognostic relevance of DE and DH/TH status among a retrospective multicentric cohort of 16 cases of pcDLBCL-LT and 17 cases of pcDLBCL-NOS. All cases were thoroughly reevaluated, both on a morphological and immunohistochemical level, and tested by means of fluorescence in situ hybridization for MYC, BCL2 and BCL6 rearrangements. DE status was observed in 69% of pcDLBCL-LT cases and in 24% of pcDLBCL-NOS cases; however, it did not impact prognosis in any of the groups examined. Combining molecular results, we highlighted a relevant fraction of DH pcDLBCL cases (three pcDLBCL-LT cases and one pcDLBCL-NOS case) and the very first case of TH pcDLBCL-LT reported to date. All DH cases were characterized by MYC and BCL6 rearrangements. Overall, DH/TH cases represented 15% (5/33) of all pcDLBCLs and were mostly pcDLBCL-LT. DH/TH status and DH status alone were associated with poorer overall survival and disease-specific survival (both p < 0.05) among all pcDLBCLs, without reaching statistical significance in the pcDLBCL-LT and pcDLBCL-NOS groups. In conclusion, MYC, BCL2, and BCL6 cytogenetical testing could be useful in identifying a putative subset of more aggressive pcDLBCLs, although this observation has to be confirmed by further studies.

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.

A Systematic Approach to the Cutaneous Lymphoid Infiltrates: A Clinical, Morphologic, and Immunophenotypic Evaluation

CONTEXT.—

The evaluation of cutaneous lymphoid infiltrates, both neoplastic and inflammatory, occurs very frequently in routine dermatopathologic examination and consultation practices. The "tough" cutaneous lymphoid infiltrate is feared by many pathologists; skin biopsies are relatively small, whereas diagnostic possibilities are relatively broad. It is true that cutaneous lymphomas can be difficult to diagnose and that in many circumstances multiple biopsies are required to establish a correct diagnostic interpretation. As a reminder, one should understand that low-grade cutaneous lymphomas are indolent disorders that usually linger for decades and that therapy does not result in disease cure. It is also important to remember that in most circumstances, those patients will die from another process that is completely unrelated to a diagnosis of skin lymphoma (even in the absence of specific therapy).

OBJECTIVE.—

To use a clinicopathologic, immunophenotypic, and molecular approach in the evaluation of common lymphocytic infiltrates.

DATA SOURCES.—

An in-depth analysis of updated literature in the field of cutaneous lymphomas was done, with particular emphasis on updated terminology from the most recent World Health Organization classification of skin and hematologic tumors.

CONCLUSIONS.—

A diagnosis of cutaneous lymphoid infiltrates can be adequately approached using a systematic scheme following the proposed ABCDE system. Overall, cutaneous T- and B-cell lymphomas are rare and "reactive" infiltrates are more common. Evaluation of lymphoid proliferations should start with a good sense of knowledge of the clinical presentation of the lesions, the clinical differential considerations, and a conscientious and appropriate use of immunohistochemistry and molecular tools.

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.

Diffuse large B-cell lymphoma variants: an update

Diffuse large B-cell lymphoma (DLBCL) is the most common type of lymphoma, representing approximately one-third of all cases worldwide. In the World Health Organization (WHO) classification of lymphomas, most cases of DLBCL are designated as not otherwise specified (NOS). About 20% of cases, however, are designated as specific variants of DLBCL. These variants, 13 in total, are specified on the basis of distinctive morphological or immunophenotypic findings or distinctive biological or clinical issues associated with their diagnoses. In this review we discuss the following variants: T-cell/histiocyte-rich large B-cell lymphoma; ALK-positive large B-cell lymphoma; plasmablastic lymphoma; intravascular large B-cell lymphoma; large B-cell lymphoma with IRF4 rearrangement; primary mediastinal large B-cell lymphoma; primary cutaneous diffuse large B-cell lymphoma, leg type; primary diffuse large B-cell lymphoma of the central nervous system; diffuse large B-cell lymphoma associated with chronic inflammation; lymphomatoid granulomatosis; primary effusion lymphoma; and HHV8-positive diffuse large B-cell lymphoma, NOS. Two additional variants recognised in the WHO classification, EBV-positive diffuse large B-cell lymphoma and EBV-positive mucocutaneous ulcer are discussed elsewhere in another review within this issue of Pathology. Although not recognised as a specific variant in the current WHO classification, primary testicular diffuse large B-cell lymphoma also has unique biological features and requires some modification of the standard treatment approach for patients with DLBCL. Therefore, we suggest that primary testicular diffuse large B-cell lymphoma also should be recognised as a specific variant of DLBCL in a future version of the WHO classification.

Large B - Cell Lymphoma of the Leg - Unfavourable Course with Rituximab/Bendamustin

BACKGROUND:

Cutaneous B-cell lymphomas represent about 25% of all cutaneous lymphomas. Peripheral diffuse large B-cell lymphoma of the leg type is the most aggressive subtype seen mainly in elderly patients. Treatment is not standardised.

CASE REPORT:

An 87-year-old female patient was presented in May 2018 because of the development of painless subcutaneous nodules on the legs since late 2017. On examination, we observed up to 5 cm large erythematous nodules on the legs and a smaller plaque in the left submammary fold. The histology of a skin demonstrated tumour infiltrate that was separated from the overlying epidermis by a grenz zone. It consisted of densely packed, blastoid lymphocytic cells with numerous, and some atypical mitoses. The cells were positive for CD20, CD79A and CD5. Almost 100% of the cells were labelled with Ki67. The diagnosis of a diffuse large B-cell lymphoma (PCLBCL-LT) of the leg was confirmed. Histologic analysis of a bone marrow biopsy demonstrated a hypercellular bone marrow without malignant lymphatic infiltrates. Diagnostic ultrasound of cervical nodes and computerised tomography (CT) scans (native and with contrast medium) of head, neck and trunk excluded an extracutaneous manifestation of the PCLBCL-LT. Treatment with rituximab plus bendamustibe was initiated, but tumour progress was noted after the second course. Suggested palliative therapy with radiation and rituximab was refused. The patient died 7 months after diagnosis.

CONCLUSIONS:

Although some trials suggested a beneficial effect of immuno-chemotherapy, the prognosis of (PCLBCL-LT) remains poor. Standardised treatment is missing due to the relative rarity of this malignancy.

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.