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Causes
By Mayo Clinic staff
Scientists don't understand the exact causes of leukemia. It seems to develop from a combination of genetic and environmental factors.
How leukemia forms
In general, leukemia occurs when some blood cells acquire mutations in their DNA — the instructions inside each cell that guide its action. The mutations cause the cell to grow and divide more rapidly and to continue living when normal cells would die. Over time, these abnormal cells can crowd out healthy blood cells, causing the signs and symptoms of leukemia.
How leukemia is classified
Doctors classify leukemia based on its speed of progression and the type of cells involved.
The first type of classification is by how fast the leukemia progresses:
- Acute leukemia. In acute leukemia, the abnormal blood cells are immature blood cells (blasts). They can't carry out their normal work, and they multiply rapidly, so the disease worsens quickly. Acute leukemia requires aggressive, timely treatment.
- Chronic leukemia. This type of leukemia involves more mature blood cells. These blood cells replicate or accumulate more slowly and can function normally for a period of time. Some forms of chronic leukemia initially produce no symptoms and can go unnoticed or undiagnosed for years.
The second type of classification is by type of white blood cell affected:
- Lymphocytic leukemia. This type of leukemia affects the lymphoid cells or lymphocytes, which form lymphoid or lymphatic tissue. Lymphatic tissue makes up your immune system.
- Myelogenous (MI-uh-loj-uh-nus) leukemia. This type of leukemia affects the myeloid cells. Myeloid cells give rise to red blood cells, white blood cells and platelet-producing cells.
Types of leukemia
The major types of leukemia are:
- Acute lymphocytic leukemia (ALL). This is the most common type of leukemia in young children. ALL can also occur in adults.
- Acute myelogenous leukemia (AML). AML is a common type of leukemia. It occurs in children and adults.
- Chronic lymphocytic leukemia (CLL). With CLL, the most common adult leukemia, you may feel well for years without treatment. CLL is very rare in children.
- Chronic myelogenous leukemia (CML). This type of leukemia mainly affects adults. A person with CML may have few or no symptoms for months or years before entering a phase in which the leukemia cells grow more quickly.
Other, rarer types of leukemia exist, including hairy cell leukemia.
- What you need to know about leukemia. National Cancer Institute. http://www.cancer.gov/cancertopics/wyntk/leukemia/allpages. Accessed Feb. 17, 2010.
- Leukemia. Leukemia & Lymphoma Society. http://www.leukemia-lymphoma.org/all_page?item_id=7026&viewmode=print. Accessed Feb. 17, 2010.
- SEER stat fact sheets: Acute lymphocytic leukemia. Surveillance Epidemiology and End Results. http://seer.cancer.gov/statfacts/html/alyl.html. Accessed Feb. 23, 2010.
- SEER stat facts sheets: Chronic lymphocytic leukemia. Surveillance Epidemiology and End Results. http://seer.cancer.gov/statfacts/html/clyl.html. Feb. 23, 2010.
- SEER stat facts sheets: Acute myeloid leukemia. Surveillance Epidemiology and End Results. http://seer.cancer.gov/statfacts/html/amyl.html. Feb. 23, 2010.
- SEER stat facts sheets: Chronic myeloid leukemia. Surveillance Epidemiology and End Results. http://seer.cancer.gov/statfacts/html/cmyl.html. Feb. 23, 2010.
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