Chapter 105. Malignancies of Lymphoid Cells (Part 3)

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General Aspects of Lymphoid Malignancies Etiology 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 in women 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) General Aspects of Lymphoid Malignancies Etiology 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 in
women and more common in whites than in blacks. This is an uncommon malignancy 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 predominantly cancers of children and young adults. The L3 or Burkitt's leukemia occurring in children in developing countries seems to be associated with infection by the Epstein-Barr virus (EBV) in infancy. However, the explanation for the etiology of more common subtypes of ALL is much less certain. Childhood ALL occurs more often in higher socioeconomic subgroups. Children with trisomy 21 (Down's syndrome) have an increased risk for childhood acute lymphoblastic leukemia as well as acute myeloid leukemia. Exposure to high-energy radiation in early childhood 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 myeloid leukemia is still much more common in older patients. Environmental exposures including certain industrial exposures, exposure to agricultural chemicals, and smoking might increase the risk of developing ALL as an adult. ALL was diagnosed in 5200 persons and AML in 13,410 persons in the United States in 2007. The preponderance of evidence suggests that Hodgkin's disease is of B cell origin. The incidence of Hodgkin's disease appears fairly stable, with 8190 new cases diagnosed in 2007 in the United States. Hodgkin's disease is more common in whites than in blacks and more common in males than in females. A bimodal distribution of age at diagnosis has been observed, with one peak incidence
occurring in patients in their twenties and the other in those in their eighties. Some of the late age peak may be attributed to confusion among entities with similar appearance such as anaplastic large cell lymphoma and T cell–rich B cell lymphoma. Patients in the younger age groups diagnosed in the United States largely have the nodular sclerosing subtype of Hodgkin's disease. Elderly patients, patients infected with HIV, and patients in third world countries more commonly have mixed-cellularity Hodgkin's disease or lymphocyte-depleted Hodgkin's disease. Infection by HIV is a risk factor for developing Hodgkin's disease. In addition, an association between infection by EBV and Hodgkin's disease has been suggested. A monoclonal or oligoclonal proliferation of EBV-infected cells in 20– 40% of the patients with Hodgkin's disease has led to proposals for this virus having an etiologic role in Hodgkin's disease. However, the matter is not settled definitively. For unknown reasons, non-Hodgkin's lymphomas increased in frequency in the United States at the rate of 4% per year between 1950 and the late 1990s. The rate of increase in the past few years seems to be decreasing. About 63,190 new cases of non-Hodgkin's lymphoma were diagnosed in the United States in 2007. Non-Hodgkin's lymphomas are more frequent in the elderly and more frequent in men. Patients with both primary and secondary immunodeficiency states are predisposed to developing non-Hodgkin's lymphomas. These include patients with
HIV infection; patients who have undergone organ transplantation; and patients with inherited immune deficiencies, the sicca syndrome, and rheumatoid arthritis.