Leukemia is classified by the type of white blood cells affected and by how quickly the disease progresses. Lymphocytic leukemia (also known as lymphoid or lymphoblastic leukemia) develops in the white blood cells called lymphocytes in the bone marrow. Myeloid (also known as myelogenous) leukemia may also start in white blood cells other than lymphocytes, as well as red blood cells and platelets.
In terms of how quickly it develops or gets worse, leukemia is classified as either acute (fast-growing) or chronic (slow-growing). Acute leukemia is rapidly progressing and results in the accumulation of immature, functionless blood cells in the bone marrow. With this type of leukemia, cells reproduce and build up in the marrow, decreasing the marrow’s ability to produce enough healthy blood cells. Chronic leukemia progresses more slowly and results in the accumulation of relatively mature, but still abnormal, white blood cells.
Types of leukemia include:
Acute lymphocytic leukemia (ALL) progresses rapidly, replacing healthy cells that produce functional lymphocytes with leukemia cells that can"t mature properly. The leukemia cells are carried in the bloodstream to other organs and tissues, including the brain, liver, lymph nodes and testes, where they continue to grow and divide. The growing, dividing and spreading of these leukemia cells may result in a number of possible symptoms.
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Acute myeloid leukemia (AML), also known as acute myelogenous leukemia, acute myeloblastic leukemia, acute granulocytic leukemia or acute nonlymphocytic leukemia, is a fast-growing form of cancer of the blood and bone marrow.
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Chronic lymphocytic leukemia (CLL) is a typically slow-growing cancer that begins in lymphocytes in the bone marrow and extends into the blood. It may also spread to lymph nodes and organs such as the liver and spleen. CLL develops when too many abnormal lymphocytes grow, crowding out normal blood cells and making it difficult for the body to fight infection.
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Chronic myeloid leukemia (CML), also known as chronic myelogenous leukemia, begins in the blood-forming cells of the bone marrow and then, over time, spreads to the blood. Eventually, the disease spreads to other areas of the body.
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Hairy cell leukemia (HCL) is a rare subtype of chronic lymphocytic leukemia (CLL) that progresses slowly. HCL is caused when bone marrow makes too many B cells (lymphocytes), a type of white blood cell that fights infection. As the number of leukemia cells increases, fewer healthy white blood cells, red blood cells and platelets are produced.
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Myelodysplastic syndromes (MDS) are a group of closely related diseases in which the bone marrow produces too few functioning red blood cells (which carry oxygen), white blood cells (which fight infection), or platelets (which prevent or stop bleeding), or any combination of the three. The different types of myelodysplastic syndromes are diagnosed based on certain changes in the blood cells and bone marrow. The cells in the blood and bone marrow (also called myelo) usually look abnormal (or dysplastic), hence the name myelodysplastic syndromes.
According to the American Cancer Society, about 13,000 people a year are diagnosed with MDS. In the past, MDS was commonly referred to as a preleukemic condition (and it is still sometimes called preleukemia) because some people with MDS develop acute leukemia as a complication of the disease. However, most patients with MDS will never develop acute leukemia.
By convention, MDS are reclassified as acute myeloid leukemia (AML) with myelodysplastic features when blood or bone marrow blasts reach or exceed 20 percent.
Learn more about the signs, symptoms and treatments of blood cancers.
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