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INTRODUCTION

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Lymphomas are a malignancy arising from lymphoid cells, with more than 60 distinct variants identified by the World Health Organization (WHO). Lymphomas can originate in B cells, T cells, or natural killer cells, and are broadly categorized into Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL). Within NHL, further differentiation is made based on clinical presentation and histology. About 85% of lymphomas in the United States and Western Europe are of B-cell origin. Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of NHL in North America and the focus of this chapter. The majority of the information in this chapter is applicable to DLBCL-NOS (not otherwise specified). Short discussions of other subtypes of diffuse large B-cell lymphoma and of other lymphomas of large B cells are included at the end of this chapter.

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EPIDEMIOLOGY

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DLBCL is a B-cell lymphoma characterized by malignant proliferations of lymphocytes at various stages during the normal B-cell maturation process and accounts for 30%-40% of all NHL cases. The annual incidence is approximately 16.5 per 100,000 people per year, with a slightly higher incidence in men compared to women (SEER). Comparing incidence based on race, Caucasians have the highest and American Indians/Alaskan Natives the lowest (SEER). The median age of diagnosis is 67 years old.

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In a majority of patients, no clear risk factor can be identified; although the proportion of Epstein-Barr virus associated DLBCL is greater in the elderly, suggesting a possible viral connection. HIV strongly increases the risk of lymphoma, with DLBCL being the most common HIV-associated lymphoid malignancy. The underlying pathophysiology is likely due to chronic antigenic stimulation causing polyclonal B-cell expansion and then subsequent emergence of monoclonal B cells. Autoimmune rheumatologic diseases, such as Sjogren's, lupus, and rheumatoid arthritis have also been associated with the development of DLBCL, especially in patients with detectable autoantibodies and substantial clinical involvement. In these diseases, chronic immune stimulation may promote lymphoma development although the role of immunosuppressive medication regimens is also being studied. Finally, a small number of patients present with histologic progression or transformation to DLBCL after a diagnosis of an indolent NHL, such as follicular lymphoma, or chronic lymphocytic leukemia. Transformation of chronic lymphocytic leukemia into diffuse large B-cell lymphoma is known as Richter's transformation.

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PATHOLOGY

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Definitive diagnosis is made via excisional biopsy or core needle biopsy (fine needle aspiration is inadequate) with hematopathologic review of slides. Microscopic examination usually demonstrates a diffuse infiltrate of large lymphoid cells completely effacing the normal nodal architecture. The neoplastic cells are large lymphocytes with nuclei greater than twice the size of small lymphocyte nuclei, prominent nucleoli, and amphiphilic to basophilic cytoplasm. Histology can reveal centroblastic and immunoblastic cell types but these distinctions are not highly reproducible and do not have clinical implications. For most DLBCL subtypes, the cells express the pan-B cell markers CD19, CD20, and CD79a. CD5 is expressed in ...

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