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

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

DISEASE OVERVIEW

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

DIAGNOSIS

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

RISK-STRATIFICATION

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

RISK-ADAPTED THERAPY

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

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.

Clinico-Pathological, Cytogenetic and Molecular Profiles of Primary Cutaneous Diffuse Large B-Cell Lymphomas

We analyzed the clinico-pathological, cytogenetic and molecular features of 18 Primary Cutaneous Diffuse Large B-Cell Lymphoma (PCDLBCL), and 15 DLBCL secondarily localized to the skin (SCDLBCL), highlighting biologic similarities and differences between the two groups. PCDLBCL were sub classified after histopathological review as PCDLBCL-Leg type (PCDLBCL-LT, 10 cases) and the PCDLBCL-not otherwise specified (PCDLBCL, NOS, 8 cases). Immunohistochemistry for Hans' algorithm markers, BCL2, and MYC was performed. The molecular study included the determination of the cell of origin (COO) by Lymph2Cx assay on Nano string platform, FISH analysis of IgH, BCL2, BCL6, and MYC genes, as well as the mutation analysis of MYD88 gene. At immunohistochemistry, BCL2 and MYC hyper expression was more frequent in LT than in NOS cases and, according to Hans' algorithm, PCDLBCL LT were mostly of the non-GC type (8/10), whereas in PCDLBCL NOS the GC type prevailed (6/8). The determination of COO using Lymph2Cx supported and further confirmed these results. At FISH analysis, all but one LT cases versus 5 out of 8 PCDLBCL NOS showed at least one gene rearrangement among IgH, BCL2, MYC or BCL6. In addition, MYD88 mutations were more frequently present in LT than in NOS subtypes. Interestingly, MYD88- mutated patients were older, with a non-GC phenotype and had worse OS, compared to MYD88 WT cases. Overall, SCDLBCL did not show, at the genetic and expression level, different profiles than PCDLBCL, even if they bear a significantly worse prognosis. At survival analysis, the most important prognostic factors in PCDLBCL patients were age and MYD88 mutation, whereas relapse and high Ki67 expression were relevant in SCDLBCL patients. Our study comprehensively analyzed the clinico-pathological and molecular features of PCDLBCL LT, PCDLBCL-NOS, and SCDLBCL, underlining the differnces among them and the importance of properly identifying these entities at the time of diagnosis.

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.

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

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

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.

Biological and Clinical Implications of Gene-Expression Profiling in Diffuse Large B-Cell Lymphoma: A Proposal for a Targeted BLYM-777 Consortium Panel as Part of a Multilayered Analytical Approach

Gene-expression profiling (GEP) is used to study the molecular biology of lymphomas. Here, advancing insights from GEP studies in diffuse large B-cell lymphoma (DLBCL) lymphomagenesis are discussed. GEP studies elucidated subtypes based on cell-of-origin principles and profoundly changed the biological understanding of DLBCL with clinical relevance. Studies integrating GEP and next-generation DNA sequencing defined different molecular subtypes of DLBCL entities originating at specific anatomical localizations. With the emergence of high-throughput technologies, the tumor microenvironment (TME) has been recognized as a critical component in DLBCL pathogenesis. TME studies have characterized so-called "lymphoma microenvironments" and "ecotypes". Despite gained insights, unexplained chemo-refractoriness in DLBCL remains. To further elucidate the complex biology of DLBCL, we propose a novel targeted GEP consortium panel, called BLYM-777. This knowledge-based biology-driven panel includes probes for 777 genes, covering many aspects regarding B-cell lymphomagenesis (f.e., MYC signature, TME, immune surveillance and resistance to CAR T-cell therapy). Regarding lymphomagenesis, upcoming DLBCL studies need to incorporate genomic and transcriptomic approaches with proteomic methods and correlate these multi-omics data with patient characteristics of well-defined and homogeneous cohorts. This multilayered methodology potentially enhances diagnostic classification of DLBCL subtypes, prognostication, and the development of novel targeted therapeutic strategies.