After studying this chapter, you should know:
The major categories of hematologic malignancies.
The types of tests that are used to diagnose hematologic malignancies.
The importance of clonality as a defining feature of these diseases.
Just as studies of hematopoiesis have been at the forefront of stem cell biology, rapid advances in our understanding of the pathogenesis of hematopoietic and lymphoid tumors have brought us into the molecular era of cancer diagnosis and therapy. Most centers now do targeted sequencing of “cancer genes” in each patient's tumor, an effort that will undoubtedly expand rapidly in the coming years. These advances have already begun to revolutionize how we diagnose and treat patients with these diseases and other cancers as well.
The accelerating rate of progress is exhilarating for workers in the field, but it creates challenges for students who are trying to grasp the basics (and authors who are trying to help them do so!). With this in mind, this chapter and the following ones are meant to serve as a primer for students new to these fascinating and clinically important diseases. Here, we provide an overview of the classification and diagnosis of hematologic malignancies. In Chapters 20–24, we delve into the pathogenesis of these malignancies, emphasizing molecular insights that have already impacted the diagnosis and treatment. In these chapters, we provide a more detailed look at the pathophysiology, clinical features, and treatment of the major types of hematologic malignancy, which include some of the most common cancers of children and adults.
NOMENCLATURE OF HEMATOLOGIC MALIGNANCIES
The names and descriptive terms used for the various hematologic malignancies reflect their origin and usual clinical behavior. Tumors composed of cells of the myeloid series (granulocytes, red cells, platelets, and their progenitors) are referred to as myeloid, myeloproliferative, or myelodysplastic, whereas tumors composed of lymphocytes or their progenitors are variously termed lymphoid, lymphocytic, lymphoblastic, or lymphoproliferative. Leukemia (literally, white blood) is applied to neoplasms that typically involve the bone marrow and the peripheral blood, whereas lymphoma is used to describe lymphoid tumors that commonly present as masses within lymph nodes or other soft tissues. Some lymphomas are named based on the resemblance of the tumor cells to a normal counterpart; for example, the malignant B cells of follicular lymphoma closely resemble the normal cells found within the B-cell follicles (also commonly referred to as germinal centers) of lymph nodes. Other descriptors relate to the natural history of the disease in question. Acute leukemias, if untreated, are lethal within weeks to several months, whereas chronic leukemias may be compatible with survival for many years without treatment.
CLASSIFICATION OF HEMATOLOGIC MALIGNANCIES
Classification systems are meant to provide a common language for the diagnosis and treatment of specific disease entities. As recently as 20 or so ...