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INTRODUCTION

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LEARNING OBJECTIVES

After studying this chapter you should understand:

  • The major categories of lymphoid neoplasms.

  • The role of genomic instability and infectious agents in the pathogenesis of lymphomas.

  • The characteristic pathologic and clinical features of chronic lymphocytic leukemia and the major subtypes of non-Hodgkin lymphoma.

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INTRODUCTION TO THE LYMPHOID NEOPLASMS

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The lymphomas, chronic lymphocytic leukemias, and plasma cell neoplasms are a group of entities that have in common an origin from mature lymphoid cells. However, in other respects, these tumors are remarkably varied in terms of their clinical presentation, behavior, molecular pathogenesis, treatment, and outcome. Historically, these tumors have been grouped according to their typical presentation and their clinical aggressiveness. This remains a useful way to think about these tumors, with the important caveat that even within a particular diagnostic category there is a range of clinical presentations and courses. In recognition of this, the current World Health Organization (WHO) classification of lymphoid neoplasms largely relies on objective pathologic and molecular features to establish specific diagnoses.

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Tumors referred to as lymphomas most commonly present as a mass within lymph nodes or other secondary lymphoid tissues but also may arise in and affect the function of virtually any organ in the body. Lymphocytic leukemias, by definition, involve the bone marrow and peripheral blood at presentation but also commonly cause lymphadenopathy and splenomegaly. As was discussed in Chapter 19, these distinctions are not absolute; virtually all tumors referred to as lymphomas present on occasion with marrow and blood involvement, and leukemias sometimes present as lymphomatous masses. Lymphomas and lymphocytic leukemias also share a propensity to cause immune dysregulation, which gives rise to:

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  • B symptoms (fever, night sweats, and weight loss).

  • Immunosuppression and susceptibility to infection.

  • Breakdown of immune tolerance, often leading to production of autoantibodies, particularly against red cells or platelets, and other manifestations of autoimmunity.

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Plasma cell tumors have their own distinctive set of signs and symptoms, which are related to destructive bone lesions, kidney failure, and the deleterious effects of complete or partial immunoglobulins secreted by the tumor cells.

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The complexity of neoplastic disorders of mature lymphocytes and plasma cells is daunting, rivaling (and reflecting) the complexity of the immune system itself. The most recent WHO classification of lymphoid neoplasms lists over 50 different types, many of which have fascinating biologic and clinical features but are too rare to merit discussion here. Instead, we will focus primarily on the more common tumors (listed in Table 22-1). This handful of neoplasms, which includes several non-Hodgkin lymphomas, chronic lymphocytic leukemia, Hodgkin lymphoma, and plasma cell neoplasms and related disorders, encompasses over 90% of human lymphoid tumors. A few uncommon disorders of exceptional pathogenic interest also will be mentioned.

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In this chapter, we present a brief overview of the pathogenesis of lymphoid neoplasms that is relevant to many of the most ...

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