Chapter 105. Malignancies of Lymphoid Cells (Part 3)

General Aspects of Lymphoid MalignanciesEtiology and Epidemiology The relative frequency of the various lymphoid malignancies is shown in Fig. 105-1. Chronic lymphoid leukemia (CLL) is the most prevalent form of leukemia in western countries. It occurs most frequently in older adults and is exceedingly rare in children. In 2007, 15,340 new cases were diagnosed in the United States, but because of the prolonged survival associated with this disorder, the total prevalence is many times higher. CLL is more common in men than inwomen and more common in whites than in blacks. This is an uncommon malignancy in Asia. The...
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Chapter 105. Malignancies of Lymphoid Cells (Part 3) Chapter 105. Malignancies of Lymphoid Cells (Part 3) General Aspects of Lymphoid Malignancies Etiology and Epidemiology The relative frequency of the various lymphoid malignancies is shown inFig. 105-1. Chronic lymphoid leukemia (CLL) is the most prevalent form ofleukemia in western countries. It occurs most frequently in older adults and isexceedingly rare in children. In 2007, 15,340 new cases were diagnosed in theUnited States, but because of the prolonged survival associated with this disorder,the total prevalence is many times higher. CLL is more common in men than inwomen and more common in whites than in blacks. This is an uncommonmalignancy in Asia. The etiologic factors for typical CLL are unknown. Figure 105-1 Relative frequency of lymphoid malignancies . In contrast to CLL, acute lymphoid leukemias (ALLs) are predominantlycancers of children and young adults. The L3 or Burkitts leukemia occurring inchildren in developing countries seems to be associated with infection by theEpstein-Barr virus (EBV) in infancy. However, the explanation for the etiology ofmore common subtypes of ALL is much less certain. Childhood ALL occurs moreoften in higher socioeconomic subgroups. Children with trisomy 21 (Downssyndrome) have an increased risk for childhood acute lymphoblastic leukemia aswell as acute myeloid leukemia. Exposure to high-energy radiation in earlychildhood increases the risk of developing T cell acute lymphoblastic leukemia. The etiology of ALL in adults is also uncertain. ALL is unusual in middle-aged adults but increases in incidence in the elderly. However, acute myeloidleukemia is still much more common in older patients. Environmental exposuresincluding certain industrial exposures, exposure to agricultural chemicals, andsmoking might increase the risk of developing ALL as an adult. ALL wasdiagnosed in 5200 persons and AML in 13,410 persons in the United States in2007. The preponderance of evidence suggests that Hodgkins disease is of B cellorigin. The incidence of Hodgkins disease appears fairly stable, with 8190 newcases diagnosed in 2007 in the United States. Hodgkins disease is more commonin whites than in blacks and more common in males than in females. A bimodaldistribution of age at diagnosis has been observed, with one peak incidenceoccurring in patients in their twenties and the other in those in their eighties. Someof the late age peak may be attributed to confusion among entities with similarappearance such as anaplastic large cell lymphoma and T cell–rich B celllymphoma. Patients in the younger age groups diagnosed in the United Stateslargely have the nodular sclerosing subtype of Hodgkins disease. Elderly patients,patients infected with HIV, and patients in third world countries more commonlyhave mixed-cellularity Hodgkins disease or lymphocyte-depleted Hodgkinsdisease. Infection by HIV is a risk factor for developing Hodgkins disease. Inaddition, an association between infection by EBV and Hodgkins disease has beensuggested. A monoclonal or oligoclonal proliferation of EBV-infected cells in 20–40% of the patients with Hodgkins disease has led to proposals for this virushaving an etiologic role in Hodgkins disease. However, the matter is not settleddefinitively. For unknown reasons, non-Hodgkins lymphomas increased in frequency inthe United States at the rate of 4% per year between 1950 and the late 1990s. Therate of increase in the past few years seems to be decreasing. About 63,190 newcases of non-Hodgkins lymphoma were diagnosed in the United States in 2007.Non-Hodgkins lymphomas are more frequent in the elderly and more frequent inmen. Patients with both primary and secondary immunodeficiency states arepredisposed to developing non-Hodgkins lymphomas. These include patients withHIV infection; patients who have undergone organ transplantation; and patientswith inherited immune deficiencies, the sicca syndrome, and rheumatoid arthritis.