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Chronic lymphocytic leukemia (CLL)
Chronic lymphocytic leukemia (CLL) is a cancer that starts in blood stem cells. Stem cells are basic cells that develop into different types of cells that have different jobs.
As the stem cells of the blood develop, they become blast cells (blasts), which are immature blood cells. In leukemia, there is an overproduction of blast cells. These blast cells develop abnormally and don’t develop into mature blood cells. Over time, the blast cells crowd out normal blood cells so that they can’t do their jobs. When leukemia is diagnosed, these blast cells may be called leukemia cells.
CLL starts in abnormal lymphoid stem cells. It is called chronic because it usually develops slowly over months or years. It is also called chronic lymphoid leukemia. In 95% of all CLLs, the abnormal lymphoid stem cells develop into cancerous (malignant) B cells, or B lymphocytes.
CLL is one of the most common types of leukemia in adults. It is less common in children.
Find out more about CLL.