Genomic Analyses Identify Recurrent Alterations in Immune Evasion Genes in Diffuse Large B-Cell Lymphoma, Leg Type

Unveiling Primary Cutaneous B-Cell Lymphomas: New Insights into Diagnosis and Treatment Strategies

BACKGROUND/OBJECTIVES

Primary cutaneous B-cell lymphomas (PCBCL) are a rare and heterogeneous group of non-Hodgkin lymphomas that are confined to the skin at diagnosis and exhibit a tendency for cutaneous recurrence. The 5th edition of the World Health Organization and the 2022 International Consensus Classification recognize three main subtypes: primary cutaneous follicle center lymphoma (PCFCL), primary cutaneous marginal zone lymphoma/lymphoproliferative disorder (PCMZL/LPD), and primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL,LT). These subtypes differ in clinical behavior, histopathologic features, immunophenotype, and molecular alterations. Diagnosis and management remain challenging for clinicians. This review aims to provide a comprehensive overview of the defining features and current treatment strategies for PCBCL.

METHODS

This narrative review synthesizes current literature on the clinical, morphologic, immunohistochemical, and molecular characteristics of PCBCL. It also evaluates the diagnostic utility of immunohistochemistry, gene expression profiling, and molecular assays, particularly in distinguishing primary cutaneous disease from secondary cutaneous involvement by systemic lymphomas.

RESULTS

PCFCL arises from germinal center B-cells and must be differentiated from nodal follicular lymphoma. PCMZL/LPD is derived from post-germinal center B-cells and is often linked to chronic antigenic stimulation. Both PCFCL and PCMZL/LPD are indolent and associated with favorable outcomes. By contrast, PCDLBCL,LT is an aggressive lymphoma characterized by genetic alterations activating the NF-κB pathway, commonly including mutations to MYD88 and CD79B. Treatment strategies vary by subtype, ranging from localized therapies for indolent lymphomas to systemic chemoimmunotherapy for aggressive PCBCL. Emerging therapies, such as Bruton tyrosine kinase inhibitors and immunoregulatory agents, are being investigated for relapsed/refractory disease.

CONCLUSIONS

PCBCL encompass distinct clinicopathologic entities with subtype-specific diagnostic and therapeutic considerations. While current management is guided by clinical behavior, significant knowledge gaps remain regarding the molecular mechanisms underlying skin tropism, immune evasion, and disease progression. Future research could focus on improving molecular characterization and developing personalized and immune-based therapies to enhance outcomes. This review consolidates current knowledge and highlights innovations aimed at advancing the diagnosis and treatment of PCBCL in clinical practice.

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.

Molecular Determinants of Sensitivity to Polatuzumab Vedotin in Diffuse Large B-Cell Lymphoma

Polatuzumab vedotin (Pola-V) is an antibody-drug conjugate directed to the CD79B subunit of the B-cell receptor (BCR). When combined with conventional immunochemotherapy, Pola-V improves outcomes in diffuse large B-cell lymphoma (DLBCL). To identify determinants of Pola-V sensitivity, we used CRISPR-Cas9 screening for genes that modulated Pola-V toxicity for lymphomas or the surface expression of its target, CD79B. Our results reveal the striking impact of CD79B glycosylation on Pola-V epitope availability on the lymphoma cell surface and on Pola-V toxicity. Genetic, pharmacological, and enzymatic approaches that remove sialic acid from N-linked glycans enhanced lymphoma killing by Pola-V. Pola-V toxicity was also modulated by KLHL6, an E3 ubiquitin ligase that is recurrently inactivated in germinal center derived lymphomas. We reveal how KLHL6 targets CD79B for degradation in normal and malignant germinal center B cells, thereby determining expression of the surface BCR complex. Our findings suggest precision medicine strategies to optimize Pola-V as a lymphoma therapeutic. Significance: These findings unravel the molecular basis of response heterogeneity to Pola-V and identify approaches that might be deployed therapeutically to enhance the efficacy of CD79B-specific tumor killing. In addition, they reveal a novel post-translational mechanism used by normal and malignant germinal center B cells to regulate expression of the BCR. See related commentary by Leveille, p. 1577 See related article by Meriranta et al.

Identifying and addressing unmet clinical needs in primary cutaneous B-cell lymphoma: A consensus-based paper from an ad-hoc international panel

Primary cutaneous B-cell lymphomas (PCBCLs) are lymphoproliferative disorders that appear on the skin without evidence of extracutaneous manifestations at the time of diagnosis. There is a lack of evidence-based guidelines for their clinical management due to the availability of very few large scale studies and controlled clinical trials. Here we present and discuss a series of major unmet clinical needs (UCNs) in the management of PCBCLs by a panel of 16 experts involved in research and clinical practice of PCBCL. The Panel produced recommendations on the appropriateness of the clinical decisions concerning the identified clinical needs and proposed research for improving the knowledge needed to solve them. Recommendations and proposals were achieved by multiple-step formalized procedures to reach a consensus after a comprehensive analysis of the scientific literature. Recommendations and proposals lay in the domain of classification uncertainties of PCBCL, optimization of diagnosis, optimization of prognosis, optimization of staging and critical issues on therapeutic strategies with particular focus on new treatments. These recommendations are intended for use not only by experts but above all by dermatologists and hematologists with limited experience in the field of PCBCLs as well as general practitioners.

Prognostic impact of MYD88 and TP53 mutations in diffuse large B Cell lymphoma

Diffuse large B cell lymphoma (DLBCL) is the most common subtype of lymphoma. It is a highly heterogeneous lymphoid neoplasm, with variations in gene expression profiles and genetic alterations. MYD88 and TP53 genes are common to be expressed and mutated in DLBCL patients with controversy regarding their role in prognosis and survival. This study aims to determine the predictive and prognostic role of MYD88 and TP53 gene mutation in DLBCL. A prospective cohort study was conducted on 50 patients who were diagnosed with DLBCL and 30 healthy individuals to assess the sensitivity and specificity of MYD88 and TP53 genetic mutations. MYD88 and TP53 gene mutations were more sensitive, specific, and accurate in predicting overall mortality and disease progression in comparison with the international prognostic index. Mutant MYD88 and TP53 showed their prognostic importance for worse objective response rates and survival outcomes. Both mutant MYD88 and TP53 were associated with worse ORR. There was a significant statistical difference for both MYD88 and TP53 with regard to 2-year PFS and 2-year OS rate. Hence, both mutant MYD88 and TP53 can be used in predicting disease progression and overall mortality.

Navigating the Heterogeneity of Follicular Lymphoma and its Many Variants: An Updated Approach to Diagnosis and Classification

Follicular lymphoma (FL) is a lymphoid neoplasm composed of follicle center (germinal center) B cells, with varying proportions of centrocytes and centroblasts, that usually has a predominantly follicular architectural pattern. Over the past decade, our understanding of FL has evolved significantly, with new recognition of several recently defined FL variants characterized by distinct clinical presentations, behaviors, genetic alterations, and biology. This manuscript aims to review the heterogeneity of FL and its variants, to provide an updated guide on their diagnosis and classification, and to describe how approaches to the histologic subclassification of classic FL have evolved in current classification schemes.

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.

ETNK1 mutation occurs in a wide spectrum of myeloid neoplasms and is not specific for atypical chronic myeloid leukemia

BACKGROUND

ETNK1 mutation has been suggested as a useful tool to support the diagnosis of atypical chronic myeloid leukemia. ETNK1 mutations, however, occur in other myeloid neoplasms.

METHODS

The authors assessed the clinicopathologic and molecular genetic features of 80 ETNK1-mutated myeloid neoplasms.

RESULTS

Thirty-seven neoplasms (46%) were classified as myelodysplastic syndrome, 17 (21%) were classified as myelodysplastic/myeloproliferative neoplasm, 14 (18%) were classified as acute myeloid leukemia, and 12 (15%) were classified as myeloproliferative neoplasm. ETNK1 mutations were detected at the first test in 96% of patients, suggesting that ETNK1 mutation is an early event in pathogenesis. ETNK1 mutations represented the dominant clone in 63% of patients and was persistently dominant in 93%. The variant allele frequencies were usually higher in acute myeloid leukemia and increased upon leukemic transformation. ETNK1 mutation was accompanied by coexisting mutations in all patients, with ASXL1 (50%), TET2 (25%), EZH2 (24%), RUNX1 (24%), and SRSF2 (24%) mutations being the most common. Neoplasms with ETNK1 mutations were associated with morphologic dysplasia, increased blasts, myelofibrosis, and noncomplex karyotypes. With a median follow-up of 16.5 months, 30 patients died, 44 had persistent disease, and four achieved complete remission after stem cell transplantation.

CONCLUSIONS

ETNK1 mutation is present in various myeloid neoplasms, often as an early event and a dominant clone and always with concurrent mutations. It may play an important role in the pathogenesis and progression of myeloid neoplasms by causing DNA damage and inducing other mutations and genomic instability, and it may serve as a potential therapeutic target. ETNK1 mutation is not disease-specific and should be interpreted with caution to classify myeloid neoplasms.

Cutaneous Lymphoma and Antibody-Directed Therapies

The introduction of monoclonal antibodies such as rituximab to the treatment of cancer has greatly advanced the treatment scenario in onco-hematology. However, the response to these agents may be limited by insufficient efficacy or resistance. Antibody–drug conjugates are an attractive strategy to deliver payloads of toxicity or radiation with high selectivity toward malignant targets and limited unwanted effects. Primary cutaneous lymphomas are a heterogeneous group of disorders and a current area of unmet need in dermato-oncology due to the limited options available for advanced cases. This review briefly summarizes our current understanding of T and B cell lymphomagenesis, with a focus on recognized molecular alterations that may provide investigative therapeutic targets. The authors reviewed antibody-directed therapies investigated in the setting of lymphoma: this term includes a broad spectrum of approaches, from antibody–drug conjugates such as brentuximab vedotin, to bi-specific antibodies, antibody combinations, antibody-conjugated nanotherapeutics, radioimmunotherapy and, finally, photoimmunotherapy with specific antibody–photoadsorber conjugates, as an attractive strategy in development for the future management of cutaneous lymphoma.

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.

Molecular classification and therapeutics in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) encompasses a wide variety of disease states that have to date been subgrouped and characterized based on immunohistochemical methods, which provide limited prognostic value to clinicians and no alteration in treatment regimen. The addition of rituximab to CHOP therapy was the last leap forward in terms of treatment, but regimens currently follow a standardized course when disease becomes refractory with no individualization based on genotype. Research groups are tentatively proposing new strategies for categorizing DLBCL based on genetic abnormalities that are frequently found together to better predict disease course following dysregulation of specific pathways and to deliver targeted treatment. Novel algorithms in combination with next-generation sequencing techniques have identified between 4 and 7 subgroups of DLBCL, depending on the research team, with potentially significant and actionable genetic alterations. Various drugs aimed at pathways including BCR signaling, NF-κB dysfunction, and epigenetic regulation have shown promise in their respective groups and may show initial utility as second or third line therapies to patients with recurrent DLBCL. Implementation of subgroups will allow collection of necessary data to determine which groups are significant, which treatments may be indicated, and will provide better insight to clinicians and patients on specific disease course.

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.

Proliferative Tumor-Infiltrating Lymphocytes' Abundance within the Microenvironment Impacts Clinical Outcome in Cutaneous B-Cell Lymphomas

Primary cutaneous large B-cell lymphoma, leg-type (PCLBCL-LT) is the most aggressive primary cutaneous B-cell lymphoma (PCBCL). Tumor microenvironment has a crucial role in tumor development, and tumor-infiltrating lymphocytes (TILs) can be targeted by immunotherapies. We characterized TILs in 20 PCBCLs to identify the tumor microenvironment features associated with clinical outcomes. We developed a seven‒multiplex immunofluorescence panel using Opal staining and image analysis using HALO software. In PCLBCL-LT, TILs were sparsely intermingled within tumor infiltrate in contrast to those in indolent PCBCL where TILs were scattered around tumor nodule edges with variable tumor infiltration. In PCLBCL-LT, TILs were composed of CD8 and CD4, whereas CD4 was predominant in indolent PCBCL. Proliferative TILs (CD3+Ki-67+ cells) were more abundant in PCLBCL-LT (P = 0.0036) than in indolent PCBCL. In PCLBCL-LT, proliferative TILs' abundance tended to be associated with better progression-free survival. These data were confirmed in a second independent cohort of 23 cases showing that proliferative TILs were more abundant in PCLBCL-LT (P = 0.0205) and that in PCLBCL-LT, high CD3+Ki-67+ cell density was associated with better progression-free survival (P = 0.002). These distinct TILs composition and distribution among PCBCL suggest that proliferative T lymphocytes represent a good prognostic factor in PCLBCL-LT and that stimulating their functions may represent a therapeutic approach.

Primary Cutaneous Diffuse Large B-Cell Lymphoma, Leg Type on the Dorsal Foot in a Senior Woman: A Case Report

Primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL-LT) is a rare variant of the cutaneous B-cell lymphomas, with rapid growth and poor prognosis. Here, we report a case of PCDLBCL-LT on the foot in a senior woman. An 81-year-old woman presented with a rapidly growing mass on her left foot, and discoloration in both lower legs over the past 2 months was analyzed. Physical examination revealed hyperpigmented macules and papules on both lower extremities and a 3.0 × 2.0 × 0.5-cm, gray-dark nodule on the dorsal surface of the left foot. Histologic observation of the punch biopsy specimen revealed a sheet of atypical large centroblast/immunoblast-like lymphocytes; diffusely and evenly distributed in the dermis; with the immunophenotypes of CD45-positive, CD20-positive, Melan A-negative, Sox10-negative, S-100-negative, and CK20-negative; and a very high Ki-67 proliferative index (>90%). Further punch biopsy specimens of papules in the patient's lower extremities and bone marrow did not reveal atypical lymphoid tissues. Positron emission tomography/computed tomography did not show any metastatic lesions in distant organs and lymph nodes. The lesion was diagnosed as PCDLBCL-LT stage T1N0M0. The patient was treated with four cycles of combined therapy of rituximab and cyclophosphamide, hydroxydaunorubicin, vincristine (Oncovin), and prednisolone and the tumor was further treated with local radiotherapy. The tumor size was significantly shrunken. Primary cutaneous diffuse large B-cell lymphoma, leg type is a rare entity on the foot, characterized by a confluent sheet of diffuse large centroblast- and or immunoblast-like B cells with B-cell immunophenotyping. The combined therapy of rituximab and cyclophosphamide, hydroxydaunorubicin, vincristine (Oncovin), and prednisolone is the first-line treatment regimen, with increased survival.

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.

Histological Transformation and Clonal Relationship of Subcutaneous Marginal Zone B-Cell Lymphoma and Diffuse Large B-Cell Lymphoma

ABSTRACT

Histological transformation (HT) is an exceptionally uncommon and poorly understood event where a low-grade or indolent B-cell lymphoma transforms into a more aggressive entity, typically diffuse large B-cell lymphoma (DLBCL). The pathogenesis is unclear; however, HT is associated with a worse prognosis. This article reports a unique case of marginal zone lymphoma (MZL) limited to skin/subcutis (confirmed with PET-CT) that subsequently developed DLBCL, followed by nodal MZL. We explored phenotypic, molecular genetic, and cytogenetic findings in subcutaneous MZL with HT to DLBCL and subsequent progression to systemic MZL. Shared clonal peaks between the tumors were demonstrated through immunoglobulin heavy chain PCR, and genomic microarray analysis revealed both unique genomic abnormalities and shared regions of copy-neutral loss of heterozygosity in all specimens. BCL-2 expression was present in the original subcutaneous MZL, lost on conversion to Primary cutaneous diffuse large B cell lymphoma (PCDLBCL)-NOS, and regained during subsequent transformation to systemic MZL. The PCDLBCL-NOS did not demonstrate FISH rearrangements for MYC, BCL2, and BCL6. Here, we describe the histologic, immunophenotypic, and cytogenetic abnormalities of the clonally related transformation of subcutaneous MZL, PCDLBCL-NOS, and eventual systemic MZL. The predominantly subcutaneous presentation of MZL may be associated with a more aggressive outcome and raises consideration for careful evaluation of patients who present with this pattern.

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.

Immune Escape Mechanisms in Intravascular Large B-Cell Lymphoma: A Molecular Cytogenetic and Immunohistochemical Study

OBJECTIVES

Intravascular large B-cell lymphomas (IVLBCLs) are rare extranodal LBCLs in which relapse is relatively frequent. We sought to further characterize potential immune escape mechanisms in IVLBCLs that newer therapies can exploit.

METHODS

A series of 33 IVLBCLs were evaluated for programmed cell death ligand 1 (PD-L1) and PD-L2 expression by immunohistochemistry (IHC), chromosomal alterations (CAs) in the PDL1/PDL2 locus by fluorescence in situ hybridization, and loss of major histocompatibility complex (MHC) class I and II expression by IHC.

RESULTS

Cases were subclassified as classical (n = 22) or hemophagocytic syndrome (HPS)-associated (n = 11) variants. A total of 12 cases (39%; n = 12/31) expressed PD-L1 and/or PD-L2. CAs were seen in 7 cases (7/29 [24%]) and included gains, amplifications, and rearrangements. CAs in classical variant cases (24%; n = 5/21) included gains (n =1), gains with concurrent rearrangements (n = 2), and amplifications (n = 2). The 2 HPS-associated variant cases with CAs (25%; n = 2/8) both showed amplification, including 1 case with a concurrent rearrangement. A majority of cases with CAs (71%; n = 5/7) were PD-L1/PD-L2 IHC positive. Among PD-L1/PD-L2 IHC-positive cases, 45% harbored a CA. Loss of MHC class I and/or class II was seen in 27% (n = 9/33) of cases.

CONCLUSIONS

Altogether, our data show that 65% (n = 20/31) of IVLBCLs may exploit immune evasion strategies through PD-L1/PD-L2 expression or downregulation of MHC proteins.

Effect of ibrutinib with R-CHOP chemotherapy in genetic subtypes of DLBCL

In diffuse large B cell lymphoma (DLBCL), tumors belonging to the ABC but not GCB gene expression subgroup rely upon chronic active B cell receptor signaling for viability, a dependency that is targetable by ibrutinib. A phase III trial ("Phoenix;" ClinicalTrials.gov: NCT01855750) showed a survival benefit of ibrutinib addition to R-CHOP chemotherapy in younger patients with non-GCB DLBCL, but the molecular basis for this benefit was unclear. Analysis of biopsies from Phoenix trial patients revealed three previously characterized genetic subtypes of DLBCL: MCD, BN2, and N1. The 3-year event-free survival of younger patients (age ≤60 years) treated with ibrutinib plus R-CHOP was 100% in the MCD and N1 subtypes while the survival of patients with these subtypes treated with R-CHOP alone was significantly inferior (42.9% and 50%, respectively). This work provides a mechanistic understanding of the benefit of ibrutinib addition to chemotherapy, supporting its use in younger patients with non-GCB DLBCL.

Molecular Pathogenesis of BCR-ABL-Negative Atypical Chronic Myeloid Leukemia

Atypical chronic myeloid leukemia is a rare disease whose pathogenesis has long been debated. It currently belongs to the group of myelodysplastic/myeloproliferative disorders. In this review, an overview on the current knowledge about diagnosis, prognosis, and genetics is presented, with a major focus on the recent molecular findings. We describe here the molecular pathogenesis of the disease, focusing on the mechanisms of action of the main mutations as well as on gene expression profiling. We also present the treatment options focusing on emerging targeted therapies.

Atypical Chronic Myelogenous Leukemia, BCR-ABL1 Negative: Diagnostic Criteria and Treatment Approaches

Atypical chronic myelogenous leukemia (aCML), BCR/ABL1 negative is a rare myelodysplastic/myeloproliferative neoplasm, usually manifested with hyperleukocytosis without monocytosis or basophilia, organomegaly, and marked dysgranulopoiesis. In this review, we will discuss the classification and diagnostic criteria of aCML, as these have been formulated during the past 30 years, with a focus on the recent advances in the molecular characterization of the disease. Although this entity does not have a definitive molecular profile, its molecular characterization has contributed to a better understanding and more accurate classification and diagnosis of aCML. At the same time, it has facilitated the identification of adverse prognostic factors and the stratification of patients according to their risk for leukemic transformation. What is more, the molecular characterization of the disease has expanded our therapeutic choices, thoroughly presented and analyzed in this review article.

Outcomes in primary cutaneous diffuse large B-cell lymphoma, leg type

Primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL, LT) is a rare, aggressive lymphoma characterized by skin involvement predominantly in the lower extremities. Immunochemotherapy with or without involved-site radiation therapy (ISRT) is considered standard front-line therapy. Over-expression of PD-L1/PD-L2 is seen in a high proportion of PCDLBCL, LT cases, but efficacy of immune checkpoint inhibitors (ICI) in relapsed/refractory, PCDLBCL, LT has not been thoroughly studied. We conducted a retrospective cohort study of patients diagnosed with PCDLBCL, LT seen at Mayo Clinic from 1 January 2000 to 31 December 2020. Using the Kaplan-Meier method, we calculated progression-free survival, duration of response, and overall survival in patients who received front-line rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) with and without ISRT, and salvage ICI therapy for relapsed/refractory disease. A total of 28 patients with PCDLBCL, LT were identified. The median PFS in patients treated with R-CHOP plus ISRT was 58 months (95% CI: 18-112) compared to 14 months (95% CI: 5-not reached; p = 0.04) in those treated with R-CHOP without ISRT. The median PFS from salvage ICI therapy was 10 months (95% CI: 4-not reached), and median DOR from salvage ICI therapy was 23 months [95% CI: 4-26]. R-CHOP with ISRT had a significantly longer median PFS compared to R-CHOP without ISRT as front-line therapy for PCDLBCL, LT. ICIs may have a role in treating relapsed/refractory disease as reasonable activity in heavily pre-treated patients was observed in this study.

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.

Genomic landscape of cutaneous follicular lymphomas reveals 2 subgroups with clinically predictive molecular features

Primary cutaneous follicle center lymphomas (PCFCLs) are indolent B-cell lymphomas that predominantly remain skin restricted and manageable with skin-directed therapy. Conversely, secondary cutaneous involvement by usual systemic follicular lymphoma (secondary cutaneous follicular lymphoma [SCFL]) has a worse prognosis and often necessitates systemic therapy. Unfortunately, no histopathologic or genetic features reliably differentiate PCFCL from SCFL at diagnosis. Imaging may miss low-burden internal disease in some cases of SCFLs, leading to misclassification as PCFCL. Whereas usual systemic FL is well characterized genetically, the genomic landscapes of PCFCL and SCFL are unknown. Herein, we analyzed clinicopathologic and immunophenotypic data from 30 cases of PCFCL and 10 of SCFL and performed whole-exome sequencing on 18 specimens of PCFCL and 6 of SCFL. During a median follow-up of 7 years, 26 (87%) of the PCFCLs remained skin restricted. In the remaining 4 cases, systemic disease developed within 3 years of diagnosis. Although the SCFLs universally expressed BCL2 and had BCL2 rearrangements, 73% of the PCFCLs lacked BCL2 expression, and only 8% of skin-restricted PCFCLs had BCL2 rearrangements. SCFLs showed low proliferation fractions, whereas 75% of PCFCLs had proliferation fractions >30%. Of the SCFLs, 67% had characteristic loss-of-function CREBBP or KMT2D mutations vs none in skin-restricted PCFCL. Both SCFL and skin-restricted PCFCL showed frequent TNFRSF14 loss-of-function mutations and copy number loss at chromosome 1p36. These data together establish PCFCL as a unique entity with biological features distinct from usual systemic FL and SCFL. We propose 3 criteria based on BCL2 rearrangement, chromatin-modifying gene mutations (CREBBP, KMT2D, EZH2, and EP300), and proliferation index to classify cutaneous FL specimens based on the likelihood of concurrent or future systemic spread.

Impact of ETNK1 somatic mutations on phosphoethanolamine synthesis, ROS production and DNA damage

Recently we showed that Ethanolamine Kinase 1 (ETNK1) mutations cause a decreased synthesis of phosphoethanolamine, and that phosphoethanolamine is able to modulate mitochondrial activity through competition with succinate for complex II. The decreased phosphoethanolamine concentration leads to increased mitochondria activity and reactive oxygen species production, which causes the accumulation of new mutations.

The MHC Class II Transactivator CIITA: Not (Quite) the Odd-One-Out Anymore among NLR Proteins

In this review, we discuss the major histocompatibility complex (MHC) class II transactivator (CIITA), which is the master regulator of MHC class II gene expression. CIITA is the founding member of the mammalian nucleotide-binding and leucine-rich-repeat (NLR) protein family but stood apart for a long time as the only transcriptional regulator. More recently, it was found that its closest homolog, NLRC5 (NLR protein caspase activation and recruitment domain (CARD)-containing 5), is a regulator of MHC-I gene expression. Both act as non-DNA-binding activators through multiple protein-protein interactions with an MHC enhanceosome complex that binds cooperatively to a highly conserved combinatorial cis-acting module. Thus, the regulation of MHC-II expression is regulated largely through the differential expression of CIITA. In addition to the well-defined role of CIITA in MHC-II GENE regulation, we will discuss several other aspects of CIITA functions, such as its role in cancer, its role as a viral restriction element contributing to intrinsic immunity, and lastly, its very recently discovered role as an inhibitor of Ebola and SARS-Cov-2 virus replication. We will briefly touch upon the recently discovered role of NLRP3 as a transcriptional regulator, which suggests that transcriptional regulation is, after all, not such an unusual feature for NLR proteins.

Epigenetic Silencing of Tumor Suppressor miR-124 Directly Supports STAT3 Activation in Cutaneous T-Cell Lymphoma

Increasing evidence supports a potential role for STAT3 as a tumor driver in cutaneous T-cell lymphomas (CTCL). The mechanisms leading to STAT3 activation are not fully understood; however, we recently found that miR-124, a known STAT3 regulator, is robustly silenced in MF tumor-stage and CTCL cells. Objective: We studied here whether deregulation of miR-124 contributes to STAT3 pathway activation in CTCL. Methods: We measured the effect of ectopic mir-124 expression in active phosphorylated STAT3 (p-STAT3) levels and evaluated the transcriptional impact of miR-124-dependent STAT3 pathway regulation by expression microarray analysis. Results: We found that ectopic expression of miR-124 results in massive downregulation of activated STAT3 in different CTCL lines, which resulted in a significant alteration of genetic signatures related with gene transcription and proliferation such as MYC and E2F. Conclusions: Our study highlights the importance of the miR-124/STAT3 axis in CTCL and demonstrates that the STAT3 pathway is regulated through epigenetic mechanisms in these cells. Since deregulated STAT3 signaling has a major impact on CTCL initiation and progression, a better understanding of the molecular basis of the miR-124/STAT3 axis may provide useful information for future personalized therapies.

ETNK1 mutations induce a mutator phenotype that can be reverted with phosphoethanolamine

Recurrent somatic mutations in ETNK1 (Ethanolamine-Kinase-1) were identified in several myeloid malignancies and are responsible for a reduced enzymatic activity. Here, we demonstrate in primary leukemic cells and in cell lines that mutated ETNK1 causes a significant increase in mitochondrial activity, ROS production, and Histone H2AX phosphorylation, ultimately driving the increased accumulation of new mutations. We also show that phosphoethanolamine, the metabolic product of ETNK1, negatively controls mitochondrial activity through a direct competition with succinate at mitochondrial complex II. Hence, reduced intracellular phosphoethanolamine causes mitochondria hyperactivation, ROS production, and DNA damage. Treatment with phosphoethanolamine is able to counteract complex II hyperactivation and to restore a normal phenotype.

Innovative Therapeutic Approaches in Primary Cutaneous B Cell Lymphoma

Background: Primary cutaneous B-cell lymphomas (pCBCL) include an infrequent group of non-Hodgkin lymphomas that are limited to skin sites at the time of diagnosis. They comprise roughly 20–25% of all cutaneous lymphomas and are subdivided into primary cutaneous marginal zone lymphoma (PCMZL), primary cutaneous follicle center lymphoma (PCFCL), and primary cutaneous diffuse large cell B cell lymphoma, leg type (PCDLCBCL, LT). The first two show a rather indolent course while PCDLCBCL, LT carries a worse prognosis. Intravascular large cell B-cell lymphoma is the most infrequent subtype, and its therapy is not covered in this review.

Topical Therapy: For solitary, single-site PCMZL and PCFCL, several topical treatment options exist. They include, but are not limited to, excision, radiotherapy, and intralesional therapies, discussed in this review. However, in selected cases, even “watchful waiting” is reasonable.

Systemic Therapy: Indolent types of pCBCL rarely require systemic treatment. However, in extended cases and more importantly DLCBCL, LT, systemic treatment is the first choice. Monoclonal anti-CD20-antibody rituximab is often used as monotherapy in PCMZL and PCFCL or combined with chemotherapy in PCDLBCL, LT. Newer options are monoclonal anti-CD40 antibody dacetuzumab, anti-PD-1 and anti-PD-L1 checkpoint inhibitors, and Bruton tyrosine kinase inhibitors.

Conclusion: Indolent pCBCL are treated with a risk-adapted strategy using intralesional steroids, RT, and interferon-α as first-line treatments. Relapsing cases may profit from rituximab. In aggressive PCDLCBCL, LT, rituximab with polychemotherapy is recommended. Innovative therapies include intralesional oncolytic virotherapy, systemic monoclonal antibodies, and small molecules.

Morphologic Patterns and the Correlation With MYD88 L265P, CD79B Mutations in Primary Adrenal Diffuse Large B-Cell Lymphoma

Primary adrenal diffuse large B-cell lymphoma (PA-DLBCL) is a rare subtype of extranodal DLBCL. Because of the rarity of this disease, its morphologic and genetic features are not comprehensively studied. Here, we systematically reviewed the clinicopathologic features of 42 cases of PA-DLBCL from our institution and investigated the frequency of MYD88 L265P and CD79B (exon 5) mutation in 29 eligible cases using Sanger sequencing. Clinically, PA-DLBCL was predominant in elderly male patients with advanced clinical stage and poor outcomes. Morphologically, the tumors often showed a sinusoidal and/or cohesive pattern with condensed chromatin and inconspicuous nucleolus which mimicked neuroendocrine carcinoma. Moreover, increased Reed-Sternberg-like cells were observed frequently. These confounding morphologic manifestations may lead to misdiagnosis. Genetically, PA-DLBCL harbored a high prevalence of MYD88 L265P (24%) and CD79B mutations (52%) which may be involved in lymphomagenesis. The CD79B mutation was significantly associated with a worse prognosis. A novel Histo-Molecular Classification system (4 categories) was proposed based on correlation with genetic changes. Generally, the neuroendocrine carcinoma-like type was associated with CD79B mutation, whereas the RS-like cell type indicated MYD88 L265P. The biphasic type was correlated with coexisting mutations of MYD88 and CD79B, whereas the common type implied no mutation. Furthermore, the common type showed significantly better survival. In conclusion, the proposed new category system could indicate the genetic changes as well as facilitate risk stratification to guide treatment and predict prognosis. Although this study augmented our understanding of PA-DLBCL, further analysis is required to validate our results and extend them to extranodal DLBCL at other sites.

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 pathogenic variant in the SETBP1 hotspot results in a forme-fruste Schinzel-Giedion syndrome

Schinzel-Giedion syndrome (SGS; OMIM 269150) is an ultra-rare genetic disorder associated with a distinctive facial gestalt, congenital malformations, severe intellectual disability, and a progressive neurological course. The prognosis for SGS is poor, with survival beyond the first decade rare. Germline, de novo heterozygous variants in the SETBP1 gene cause SGS with the pathogenic variants associated with the SGS phenotype missense and confined to exon 4 of the gene, clustered in a four amino acid (12 bp) hotspot in the SKI homologous region of the SETBP1 protein. We report a patient with a de novo I871S variant within the SKI homologous region, which has been associated with the severe phenotype previously; but our patient has fewer features of SGS and a milder course. This is the first report of a forme-fruste phenotype in a patient with a pathogenic variant within the SGS hotspot on the SETBP1 gene and it highlights the importance of considering atypical clinical presentations in the context of severe ultra-rare genetic disorders.

A Probabilistic Classification Tool for Genetic Subtypes of Diffuse Large B Cell Lymphoma with Therapeutic Implications

The development of precision medicine approaches for diffuse large B cell lymphoma (DLBCL) is confounded by its pronounced genetic, phenotypic, and clinical heterogeneity. Recent multiplatform genomic studies revealed the existence of genetic subtypes of DLBCL using clustering methodologies. Here, we describe an algorithm that determines the probability that a patient's lymphoma belongs to one of seven genetic subtypes based on its genetic features. This classification reveals genetic similarities between these DLBCL subtypes and various indolent and extranodal lymphoma types, suggesting a shared pathogenesis. These genetic subtypes also have distinct gene expression profiles, immune microenvironments, and outcomes following immunochemotherapy. Functional analysis of genetic subtype models highlights distinct vulnerabilities to targeted therapy, supporting the use of this classification in precision medicine trials.

MYD88 mutations identify a molecular subgroup of diffuse large B-cell lymphoma with an unfavorable prognosis

The 2016 World Health Organization classification defines diffuse large B-cell lymphoma (DLBCL) subtypes based on Epstein-Barr virus (EBV) infection and oncogenic rearrangements of MYC/BCL2/BCL6 as drivers of lymphomagenesis. A subset of DLBCL, however, is characterized by activating mutations in MYD88/CD79B We investigated whether MYD88/CD79B mutations could improve the classification and prognostication of DLBCL. In 250 primary DLBCL, MYD88/CD79B mutations were identified by allele-specific polymerase chain reaction or next-generation-sequencing, MYC/BCL2/BCL6 rearrangements were analyzed by fluorescence in situ hybridization, and EBV was studied by EBV-encoded RNA in situ hybridization. Associations of molecular features with clinicopathologic characteristics, outcome, and prognosis according to the International Prognostic Index (IPI) were investigated. MYD88 and CD79B mutations were identified in 29.6% and 12.3%, MYC, BCL2, and BCL6 rearrangements in 10.6%, 13.6%, and 20.3%, and EBV in 11.7% of DLBCL, respectively. Prominent mutual exclusivity between EBV positivity, rearrangements, and MYD88/CD79B mutations established the value of molecular markers for the recognition of biologically distinct DLBCL subtypes. MYD88-mutated DLBCL had a significantly inferior 5-year overall survival than wild-type MYD88 DLBCL (log-rank; P=0.019). DLBCL without any of the studied aberrations had superior overall survival compared to cases carrying ≥1 aberrancy (log-rank; P=0.010). MYD88 mutations retained their adverse prognostic impact upon adjustment for other genetic and clinical variables by multivariable analysis and improved the prognostic performance of the IPI. This study demonstrates the clinical utility of defining MYD88-mutated DLBCL as a distinct molecular subtype with adverse prognosis. Our data call for sequence analysis of MYD88 in routine diagnostics of DLBCL to optimize classification and prognostication, and to guide the development of improved treatment strategies.

Characterisation of tumour microenvironment and immune checkpoints in primary central nervous system diffuse large B cell lymphomas

Primary central nervous system diffuse large B cell lymphoma (PCNS-DLBCL) is a rare and aggressive entity of diffuse large B cell lymphoma (DLBCL). Elements of the tumour microenvironment (TME) including tumour-infiltrating lymphocytes (TILs) and tumour-associated macrophages (TAMs) have been associated with survival in DLBCL but their composition and prognostic impact in PCNS-DLBCL are unknown. Programmed cell death-1 (PD1)/programmed death-ligand 1 (PD-L1) immune checkpoint may represent a therapeutic option. Here, we aimed to characterise PD1/PDL1 immune checkpoints and the composition of the TME in PCNS-DLBCL. We collected tumour tissue and clinical data from 57 PCNS-DLBCL and used immunohistochemistry to examine TAMs (CD68, CD163), TILs (CD3, CD4, CD8, PD1) and tumour B cells (PAX5/PDL1 double stains, PDL1). The PDL1 gene was evaluated by fluorescence in situ hybridization (FISH). PAX5/PDL1 identified PDL1 expression by tumour B cells in 10/57 cases (17.5%). PDL1 gene translocation was a recurrent cytogenetic alteration in PNCS-DLBCL (8/47.17%) and was correlated with PDL1 positive expression in tumour B cells. The TME consisted predominantly of CD163 (+) M2 TAMs and CD8 (+) TILs. Most TAMs expressed PDL1 and most TILs expressed PD1. The density of TAMs and TILs did not associate with outcome. We showed that expression of PD1 on TILs and PDL1 on TAMs, but not the expression of PDL1 on tumour B cells was correlated with better prognosis. These findings support a significant role of TME composition and PD1/PDL1 crosstalk in PCNS-DLBCL pathogenesis and bring new insights to the targeted therapy of this aggressive lymphoma.

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.

Genetic alterations and their clinical implications in DLBCL

Diffuse large B cell lymphoma (DLBCL) is a highly heterogeneous lymphoid neoplasm with variations in gene expression profiles and genetic alterations, which lead to substantial variations in clinical course and response to therapy. The advent of high-throughput genome sequencing platforms, and especially whole-exome sequencing, has helped to define the genetic landscape of DLBCL. In the past 10 years, these studies have identified many genetic alterations in DLBCL, some of which are specific to B cell lymphomas, whereas others can also be observed in other types of cancer. These aberrations result in altered activation of a wide range of signalling pathways and other cellular processes, including those involved in B cell differentiation, B cell receptor signalling, activation of the NF-κB pathway, apoptosis and epigenetic regulation. Further elaboration of the genetics of DLBCL will not only improve our understanding of disease pathogenesis but also provide further insight into disease classification, prognostication and therapeutic targets. In this Review, we describe the current understanding of the prevalence and causes of specific genetic alterations in DLBCL and their role in disease development and progression. We also summarize the available clinical data on therapies designed to target the aberrant pathways driven by these alterations.

Cutaneous Lymphomas

Primary cutaneous lymphomas are the second most common form of extra-nodal lymphomas. They have special characteristics compared with other lymphomas. They are most frequently of T-cell origin and they generally have a much more indolent course than lymphomas of similar histology in other locations. Mycosis fungoides is the most common type of cutaneous lymphoma. Primary cutaneous lymphomas remain confined to the skin for a long time. Skin-directed therapies are the main treatments; systemic treatments are not very effective for the skin lesions. Skin-directed therapies used for the early and thin lesions are topical corticosteroids, phototherapy and topical retinoids and, for the more widespread or thick lesions, topical nitrogen mustard and radiation. Radiation therapy is highly effective and is indicated in virtually all cases of localised disease. Radiation therapy may be given to the whole skin surface, so-called total skin electron beam therapy. However, if the disease spreads to other organs, systemic treatments are indicated, often combined with skin-directed therapies. Conventional cytotoxic therapy is less effective in cutaneous lymphomas. The commonly used therapies, such as interferon, enhanced anti-tumour immunity and the recent advances in immune therapies may improve our treatments for cutaneous lymphomas.

Mutations of the B-Cell Receptor Pathway Confer Chemoresistance in Primary Cutaneous Diffuse Large B-Cell Lymphoma Leg Type

Primary cutaneous diffuse large B-cell lymphoma, leg type (PCLBCL-LT) preferentially involves the lower limb in elderly subjects. A combination of polychemotherapy and rituximab has improved prognosis. However, about 50% of patients will experience progression or relapse without any predictive biologic marker of therapeutic response. The mutational profile of PCLBCL-LT has highlighted mutations contributing to constitutive NF-κB and B-cell receptor (BCR) signaling pathways but has not demonstrated clinical utility. Therefore, the mutational status of 32 patients with PCLBCL-LT (14 patients with complete durable response and 18 patients with relapsing or refractory disease) was determined with a dedicated lymphopanel. Tumor pairs at diagnosis and relapse or progression were analyzed in 14 relapsing or refractory patients. Patients with PCLBCL-LT harboring one mutation that targets one of the BCR signaling genes, CD79A/B or CARD11, displayed a reduced progression-free survival and specific survival (median 18 months, P = 0.002 and 51 months, P = 0.03, respectively, whereas median duration in the wild-type group was not reached) and were associated with therapeutic resistance (P = 0.0006). Longitudinal analyses revealed that MYD88 and CD79B were the earliest and among the most mutated genes. Our data suggest that evaluating BCR mutations in patients with PCLBCL-LT may help to predict first-line therapeutic response and to select targeted therapies.