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carcinogens as radon, asbestos, beryllium, silica, arsenic, and secondhand smoke; family history; and diet (ACS, 2007g).

Leukemias (ICD-10 C91-95)

Leukemias are malignant diseases that arise from precursor cells of white blood cells. An estimated 44,240 new cases of and 21,790 deaths from leukemia were expected in 2007 in the United States, accounting for about 3.1% of all cancer diagnoses and 3.9% of all cancer deaths (ACS, 2007b). In 2004, there were 12.0 new cases of leukemia per 100,000 people in the United States (15.4 in men and 9.5 in women) and 7.2 deaths per 100,000 (9.7 in men and 5.5 in women) (Ries et al., 2007).

Although all leukemias originate in the bone marrow, there are four main types, classified by the type and developmental stage of the cells involved. Leukemias can be acute—in which case the cells grow rapidly and are not able to mature—or chronic—in which case the cells grow and accumulate slowly and look mature. And leukemias can affect different types of cells: lymphocytic leukemias affect the lymphocytes, white blood cells that make up lymphoid tissue, and myeloid leukemias affect granulocytes or monocytes, white blood cells that circulate and protect the body against infection (ACS, 2007k). Acute lymphocytic leukemia affects children more frequently than adults, whereas chronic lymphocytic leukemia affects only adults, mostly over the age of 40 years (ACS, 2007d,f). Acute myeloid leukemia, also called acute nonlymphocytic leukemia, is the most common leukemia and usually affects adults, particularly men, although it can occur in children (ACS, 2007e). Chronic myeloid leukemia affects mostly adults and is rare in children (ACS, 2007a). The four types of leukemias can be divided into subtypes based on progression and cell subtypes.

Characterizing leukemia cases gathered retrospectively for epidemiologic studies and integrating the results of studies conducted over several decades are particularly challenging because successive diagnostic criteria, with corresponding groupings and nomenclature, have been used. Individual leukemias may have unique etiologic factors (for example, T-cell leukemia is caused by the retrovirus HTLV-I), but the recognized risk factors for leukemias in general include exposure to ionizing radiation or some chemicals (such as occupational exposure to benzene or chemotherapy with alkylating agents), some genetic conditions (such as some chromosomal abnormalities, including Down syndrome), and particular acquired blood diseases (for example, myelodysplastic syndromes may develop into acute myeloid leukemia) (NCI, 2003).

Lymphomas (ICD-10 C81-85)

This section discusses two types of lymphomas: Hodgkin’s disease (HD; also called Hodgkin lymphoma) (ICD-10 C81) and non-Hodgkin lymphoma (NHL)

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