The initial evaluation of leukemia is initially made by:
1. Noting the onset of symptoms
2. Analyzing the complete blood count (CBC) results
3. Observing the type of cell that predominates (cell lineage)
Because leukemia is a disease of the bone marrow that causes normal bone marrow cell production to be crowded out as the abnormal, neoplastic cells take over, the CBC results will commonly show a decreased red cell count or anemia, as well as a decrease in platelets or thrombocytopenia. The level of anemia and thrombocytopenia tends to be more severe in acute leukemia. Leukocytosis is a hallmark feature of chronic leukemia, and because the spleen also becomes a site of extramedullary (outside of the bone marrow) hematopoiesis, prominent hepatosplenomegaly is most often associated with chronic leukemia.
The type of cell that predominates in the peripheral blood and the bone marrow is defined according to cell lineage as either myeloid or lymphoid. The myeloid stem cell gives birth to granulocytes, monocytes, megakaryocytes, and erythrocytes (see Fig. 2.3). Therefore, as will be described in the various sections of this chapter, the myeloid leukemias can involve proliferation of any stage of these four cell lines. By contrast, the lymphoid stem cell gives rise solely to lymphocytic lineage cells.
Cell maturity can be used to separate the initial diagnosis between acute and chronic leukemias. When blasts or other immature cells predominate, the leukemia is classified as acute, versus the predominance of more mature cell types being associated with chronic leukemia.
The onset of acute versus chronic leukemia is distinctly different. Acute leukemia has a quick onset, whereas chronic leukemia has a slow, insidious course and may even be discovered on routine physical examination. Age is another factor that is often consistent in the different leukemic variants. Although acute leukemia may occur at any age, chronic leukemia is usually a disease seen in adults (Table 11.1).
To summarize, using both the cell lineage and the maturity of cells that predominate, leukemias can be categorized into four broad groups:
1. Acute myeloid leukemias
2. Acute lymphoblastic leukemias
3. Chronic myelocytic leukemias (see Chapter 12)
4. Chronic lymphocytic leukemias (see Chapter 13)
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