Elsevier

Pathology

Volume 50, Issue 1, January 2018, Pages 74-87
Pathology

Review: 50th anniversary issue
Diffuse large B-cell lymphoma

https://doi.org/10.1016/j.pathol.2017.09.006Get rights and content

Summary

Diffuse large B cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma worldwide, representing approximately 30–40% of all cases in different geographic regions. Patients most often present with a rapidly growing tumour mass in single or multiple, nodal or extranodal sites. The most common type of DLBCL, designated as not otherwise specified, represents 80–85% of all cases and is the focus of this review. There are also rare types of lymphoma composed of large B-cells, in aggregate about 15–20% of all neoplasms that are sufficiently distinctive to recognise separately. DLBCL not otherwise specified (referred to henceforth as DLBCL) is a heterogeneous entity in terms of clinical presentation, genetic findings, response to therapy, and prognosis. A major advance was the application of gene expression profiling (GEP) to the study of DLBCL which further clarified this heterogeneity and provided a rationale for subdividing cases into groups. The most popular system divides cases of DLBCL according to cell-of-origin into germinal centre B-cell like (GCB) and activated B-cell like (ABC) subtypes, with about 10–15% of cases being unclassifiable. Patients with the GCB subtype usually have better prognosis than patients with the ABC subtype. Although cell-of-origin is useful for predicting outcome, the GCB and ABC subtypes remain heterogeneous, with better and worse prognostic subsets within each group. Next generation sequencing (NGS) analysis of DLBCL has facilitated global identification of numerous and diverse genetic abnormalities in these neoplasms and has shown that GCB and ABC tumours have different mutation profiles. Although the therapy of patients with DLBCL is an active area of research, the current 5-year overall survival rate is 60–70% using standard-of-care frontline therapy. A precision medicine approach for the design of new therapies based on molecular findings in DLBCL is likely the best path forward. As pathologists, our role has expanded beyond diagnosis. We must perform a complete work-up of DLBCL cases. In addition to our traditional role in establishing the diagnosis, we need to analyse markers that provide information regarding prognosis and potential therapeutic targets. We also must ensure that adequate tissue is triaged for molecular studies which are essential for designing therapy regimens, particularly in the setting of disease relapse.

Introduction

The first issue of Pathology was published in 1969. At that time lymphoma pathology and classification systems were based on morphological findings. The lineage and genetics of diffuse large B-cell lymphoma (DLBCL) were unknown and these neoplasms had been designated by a variety of names in the past century. In 1969, the classification system by Henry Rappaport was in widespread use and in this system DLBCL was known as diffuse histiocytic lymphoma.1 However, many advances in the immunology arena were being made about this time showing that the immune system is highly complex and composed of B-, T-, and natural killer cell lymphocytes as well as numerous lymphocyte subsets with diverse functions. There were also a few markers that were being applied to the study of normal lymphocytes and lymphomas, such as sheep erythrocyte rosettes (E rosettes, CD2), polyclonal immunoglobulin antibodies, and mouse EAC (erythrocyte and complement) rosettes. In 1973, using these markers, Collins and colleagues2 showed that Sternberg sarcoma (now T-lymphoblastic lymphoma) was of T-cell lineage and, in 1974, Jaffe et al. showed that follicular lymphoma was of B-cell lineage.3

Also about this time, lymphoma classifications were proposed that attempted to incorporate the new knowledge of the functional immune system. The European Lymphoma Club, led by Karl Lennert, proposed the Kiel classification and Lukes and Collins proposed their classification.4, 5 Both of these classifications were based on immunological concepts and lymphoma classification would never again rely purely on morphological findings. As reviewed by Taylor and Hartsock,6 the advent of hybridoma technology resulting in the widespread availability of monoclonal antibodies, followed by the application of molecular genetics to the study of lymphomas, initially single gene studies and subsequently high throughput methods of analysis, led to a recognition and much deeper understanding of lymphomas, including DLBCL.7 In this review we focus on DLBCL not otherwise specified (henceforth referred to as DLBCL).

Section snippets

2016 world health organization classification of DLBCL

The current consensus classification for lymphomas is the fourth edition of the World Health Organization (WHO) classification which was revised in 2016.8, 9 DLBCL is defined as a neoplasm of large B-cells arranged in a diffuse pattern. Large size is defined by the lymphoma cells being larger than the nuclei of benign histiocytes in the same tissue section.8 As this definition is based largely on morphological findings and B-cell lineage it is somewhat ‘old fashioned’ compared with the

Clinical presentation

DLBCL is the most common type of non-Hodgkin lymphoma, worldwide and in the United States.10, 11 The incidence rate is 6.3% with an estimated 25,380 new cases in the United States in 2016.11 DLBCL is more prevalent in elderly patients with a median age in the 7th decade, although it also occurs in young adults and rarely in children. There is a slight male predominance. Clinically, most patients present with a rapidly growing tumour mass involving one or more lymph nodes and extranodal sites.8,

Morphology

The name diffuse large B-cell lymphoma is self-explanatory. The lymphoma cells are large and arranged in a diffuse pattern that totally or partially effaces normal nodal or extranodal architecture.15 Fine fibrosis may compartmentalise groups of lymphoma cells or the neoplasm may be associated with sclerosis. Areas of geographic necrosis may be present. Single cell apoptosis can be prominent and the mitotic rate may be high. About 10% of cases of DLBCL are associated with a starry sky pattern.

Immunophenotype

Immunophenotypic evaluation is required to establish the diagnosis of DLBCL and can be performed by either immunohistochemistry or flow cytometry. The neoplastic cells of DLBCL express pan B cell antigens such as CD19, CD20, and CD22 as well as B-cell transcription factors including PAX5, BOB.1 and OCT2 (Fig. 2).14, 15 About 50–70% of cases of DLBCL express surface or cytoplasmic immunoglobulin, most often IgM followed by IgG and IgA.17 However, at least a third of DLBCL cases are negative for

Cytogenetic findings and antigen receptor gene rearrangements

Conventional cytogenetic analysis is helpful in the work-up of cases of DLBCL as the results provide a global view of chromosomal abnormalities. In general, complex karyotypes are more common in tumours that are clinically aggressive or resistant to therapy. Comparative genomic hybridization (CGH) applied to the study of DLBCL has shown even greater complexity with numerous gains and losses of chromosome loci in a myriad of combinations.20, 21, 22 Specific gains and losses have been shown to

Gene expression profiling

Alizadeh and colleagues27 were among the first to apply gene expression profiling (GEP) methods to the study of DLBCL and they divided cases into GCB (40–50%) and ABC (50–60%) subtypes as well as a small (∼10–15%) unclassifiable group. In patients with DLBCL treated with CHOP therapy, those with GCB neoplasms had a better survival than those with ABC tumours. Subsequently, this observation was confirmed in DLBCL patients treated with R-CHOP.28 Over time, GCB versus ABC cell-of-origin

Tumour microenvironment

The microenvironment of lymphoma cells, in other words, their interaction with host inflammatory cells, is also important in pathogenesis. Lenz and colleagues divided gene expression signatures in DLBCL into three groups: germinal centre B-cell, stromal-1 and stromal-2.31 The stromal-1 signature (prognostically favourable) is reflective of extracellular matrix deposition and histiocyte infiltration. In contrast, the stromal-2 signature (unfavourable) reflects tumour blood vessel density.

Next generation sequencing

It has been known for a number of years, as shown by using single gene assessment methods, that gene mutations or deletions play a role in the pathogenesis of cases of DLBCL. Next generation sequencing (NGS) approaches have greatly enhanced our understanding of DLBCL cases by enabling comprehensive identification of genetic alterations in cases of DLBCL. An average of 75–90 mutations per neoplasm (in some cases well over 100 mutations) has been shown. Data suggest that DLBCL cells undergo

Prognosis and special subgroups of DLBCL

As shown above, DLBCL is a highly heterogeneous group of neoplasms and patients have a variable clinical course and prognosis. Part of the task of the management of patients with DLBCL is to distinguish patients who will do well being treated with standard therapy versus patients who will not and who may benefit from more aggressive therapy. A number of tools have been developed to better stratify the risk of DLBCL patients, and some prognostic factors have been demonstrated in Fig. 3.

Treatment

A detailed discussion of the treatment of patients with DLBCL is beyond the scope of this review. The writers do not have expertise in this field and it is assumed that most readers of Pathology do not treat patients with DLBCL. Here we attempt to review some of the overall concepts involved in treating DLBCL patients.

The standard therapy for patients with DLBCL is rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP). Using this regimen, approximately 60–70% of

Diagnostic work-up

Cases of DLBCL require a complete work-up including morphological assessment, immunophenotypic analysis, cytogenetic analysis (conventional methods and FISH), and molecular diagnostic assays to assess to various gene mutations or copy number alterations (Fig. 5). Unless otherwise specified, every test discussed in this section needs to be performed.

Cell-of-origin classification can be performed using immunohistochemical algorithms at this time, but may be replaced in the future by GEP performed

Conclusion

In the diagnosis of all lymphomas including DLBCL much has changed since Pathology published its first issue in 1969. Our knowledge of the clinical, morphological and immunophenotypic spectrum of DLBCL and the molecular pathogenesis of DLBCL have greatly expanded. This knowledge is being translated into the design of novel treatment strategies and the development of novel therapeutic agents.

The current standard therapy for patients with DLBCL is the R-CHOP regimen and about 60–70% of patients

Conflicts of interest and sources of funding

The authors state that there are no conflicts of interest to disclose.

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