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Leukemia is a cancer of the blood. Leukemia begins when normal blood cells change and grow uncontrollably. Chronic lymphocytic leukemia (CLL) is a cancer of the lymphocytes, a type of white blood cell involved in the body's immune system. For about half of people with CLL, the disease grows and progresses slowly, and it may take years for symptoms to appear or for treatment to be needed. In fact, some patients may never need treatment for their CLL. The other half of people who develop CLL have a type of CLL that grows more quickly and need treatment sooner.
Lymphocytes circulate in the blood stream and are made in the lymph nodes, spleen, and bone marrow (the spongy, red tissue in the inner part of the large bones). There are three different types of lymphocytes: T cells, B cells, and natural killer (NK) cells. Generally, T cells fight infections by triggering other cells in the immune system and by destroying infected cells, B cells make antibodies, and NK cells fight microbes and cancer cells.
In people with CLL, the abnormal cells crowd other types of cells in the bone marrow, preventing the production of red blood cells (which carry oxygen), other types of normal white blood cells (neutrophils or granulocytes that fight infection), and platelets (small cells in the blood needed for clotting). This means that people with CLL may be anemic (low levels of red blood cells), more likely to get infections (because they do not have enough of the white blood cells called neutrophils that fight bacteria), and bruise or bleed easily (because of a low level of platelets)
There are two general types of CLL, and it is important for doctors to find out whether the disease is caused by the overgrowth of T cells or B cells. The T-cell type of CLL, (now called T-cell prolymphocytic leukemia) is much less common (about 1% of people with CLL have this type) than the B-cell type of the disease (more than 95% of people with CLL have the B-cell type).
Most often, CLL is diagnosed when too many abnormal lymphocytes are found in the blood. However, the same disease can occur when the abnormal lymphocytes are mostly in the lymph nodes but not in the blood. This is called small lymphocytic lymphoma, but behaves very similarly to CLL.
Find out more about basic cancer terms used in this section.
Looking for More of an Overview?
If you would like additional introductory information, explore these related items on Cancer.Net:
- ASCO Answers Fact Sheet: Read a one-page face sheet (available in PDF) that offers an easy-to-print introduction for this type of cancer.
- Cancer.Net Patient Education Video: View a short video led by an ASCO expert in this type of cancer that provides basic information and areas of research.
- Cancer.Net En Español: Read about CLL in Spanish. Infórmase sobre leucemia linfocítica crónica en español.
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