Chapter 11. Lymphoma Classification and Staging
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314 CHAPTER 11 Lymphoma Classification and Staging In this chapter I discuss the different types of lymphoma. I describe the system currently used to classify the lymphomas and discuss the individual types of lymphoma in some detail. I also describe how the stage of disease—which defines how far lymphoma has spread through a person’s body—is determined. This is the most difficult chapter in the book: lymphoma classification has always been controversial and is considered confusing even by general oncologists. However, obtaining a detailed knowledge of the specific form of their disease is often helpful to people who want to understand, as much as possible, what’s going on. Knowing which form of the disease you have, and something about the biology of the malignant cells and the clinical characteristics of that form of lymphoma, will also help you determine whether new therapies you hear about are likely to be helpful for you. The material in Chapters 9 and 10 will be helpful as background to the material in this chapter. The Different Types of Lymphoma There are over twenty different clinical entities—or specific diseases— known as lymphoma. These different kinds of lymphoma can be distinguished from one another by various characteristics, including the appearance of the malignant cells under a microscope (known as their histological appearance or their morphology), the specific proteins that appear on the cell surface, the pattern in which the cells grow, the sites in the body that are likely to be affected, the population of people most likely to be affected, Lymphoma Classification and Staging 315 V and the typical course of the disease. All the lymphomas are cancers that develop from lymphocytes; however, the different lymphomas resemble different types of lymphocytes at different developmental stages (see Chapter 10) and carry characteristic genetic mutations (see Chapter 9 and below). Perhaps the most fundamental of these distinctions is the cell type. Lymphomas can arise from B cells, T cells, or natural killer (NK) cells. The different B-cell, T-cell, and NK-cell lymphomas are distinguished from each other by how closely they resemble normal lymphocytes at different stages of development. For instance, the follicular lymphomas resemble germinal center B cells, while lymphoplasmacytic lymphomas resemble a B cell at a late stage of development—just before the transformation into a plasma cell. The different lymphomas are also distinguished by different mutations. For instance, both follicular large cell lymphoma and diffuse large B-cell lymphoma correspond to centroblasts (see Chapter 10); the specific characteristics of these diseases depend on the specific genetic abnormalities found in the malignant cells. Accurately classifying the different types of lymphoma is important for several reasons. First, different kinds of lymphoma follow different clinical courses—some grow very slowly and can safely be followed by “watching and waiting,” while others grow rapidly and need to be treated right away (see below, in the section on the WHO classification system). Second, different types of lymphoma respond to different treatment regimens: they are more or less responsive to radiation therapy or to specific chemotherapy regimens. Finally, effective use of monoclonal antibody therapy—which is directed against specific proteins manufactured by the lymphoma cells— critically depends on appropriate classification of the disease. Classification Systems Classifying all these different but closely related diseases has been a complex task. Over the years, physicians and researchers developed various classification systems, which have changed as researchers uncovered more information about both normal lymphocytic behavior and the specific forms of the disease. The concept of lymphoma as a distinct disease (or group of related diseases ) involving the lymphatic system emerged in the nineteenth century. Thomas Hodgkin, who wrote a paper in 1832 “on some morbid appearances of the absorbent glands and spleen,” recognized what we would now U 316 Understanding Lymphoma call “lymphoma” as a disease characterized by enlargement of the lymph nodes and spleen. Initially, physicians focused on the clinical course of the disease (how it progressed in patients) and “macroscopic” appearance (for instance, enlarged lymph nodes) in defining the lymphoid disorders. During the twentieth century, classification schemes based on the microscopic appearance (histology) of the malignant cells became prominent. The hope of such classification schemes is that the histological appearance of the cells will make it possible to distinguish distinct diseases that respond predictably to given therapeutic regimens. For any such classification system to function properly, the histological distinctions must be clearly recognizable (different pathologists viewing the same set of slides must come up with the...


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