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What is leukemia?

Leukemia is cancer of the blood and bone marrow. It develops when bone marrow, which produces blood cells, forms abnormal white blood cells that divide out of control. Normal white blood cells are the body's infection fighters, but these abnormal white blood cells, called leukemia cells, don't die at the same rate as normal blood cells. Instead, they accumulate and crowd out normal cells, like red blood cells, platelets, and normal white blood cells and their precursors, in the bone marrow. This can lead to difficulty getting enough oxygen to tissues (anemia), excess bleeding, and repeated infections.

Over time, leukemia cells can spread through the bone marrow and bloodstream, where they continue to divide, sometimes forming tumors and damaging organs. The organs affected depend on the type of leukemia. For example, the spleen, liver, and lymph nodes may become enlarged and swollen with the abnormal cells. Sometimes, leukemia cells reach the central nervous system (the brain and spinal cord) and build up in the cerebrospinal fluid.

In the United States, more than 43,000 adults and 5,000 children are diagnosed each year with leukemia. While exposure to radiation, benzene, and some anticancer drugs have been shown to increase the risk of developing leukemia, and a few cases are associated with genetic disorders or rare viral infections, the cause of most leukemias is not known.

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