Leukemia is a type of cancer that results in the body making too many abnormal white blood cells. This uncontrolled production results in an excessive amount of white blood cells that may be immature (acute leukemia) or mature (chronic leukemia). The leukemic cells may not function well to fight infection and may interfere with the production of red blood cells (which carry oxygen) and platelets (which control bleeding).
Normally, white blood cells play an important role in the body's natural defense system. They target and destroy foreign invaders like viruses and bacteria. White blood cells are made in the marrow (the spongy core) of your bones. Without healthy and functioning white blood cells, the body is at risk of developing severe and sometimes fatal infections.
For most people with leukemia, there's no way to identify what causes it. In some cases, though, specific risk factors can be identified:
- previous chemotherapy or radiation therapy
- exposure to high doses of radiation or to benzene (found in unleaded gasoline, tobacco smoke, the chemical industry)
- family history
- genetic abnormality, such as an abnormality on chromosome 22 (also known as the Philadelphia chromosome)
- genetic disorders, such as Down syndrome and Fanconi anemia
All forms of cancer that can spread within the body (malignant), including leukemia, are thought to be due to genetic abnormalities (mutations). In leukemia, the damage occurs in the bone marrow stem cells. These special cells help to manufacture all the other cells in the blood. With this condition the production of these cells is out of control.
Different types of leukemia
Acute leukemia develops within days to weeks, and large numbers of immature cells called "blasts" build up. These cells can't function as well as normal white blood cells, so people with acute leukemia are at a higher risk of infection. Because the body is so busy producing "blasts," it can't make as many red blood cells or platelets, which can cause anemia and bleeding disorders.
Chronic leukemia, which progresses over the course of months to years, involves overproduction of mature white blood cells that cannot function like normal white blood cells.
The four types of leukemia are:
- Acute lymphocytic leukemia (ALL) is the most common form of leukemia in children. It is the result of an uncontrolled production of a type of white blood cell called lymphocytes. This causes a buildup of the immature forms of lymphocytes. The high numbers also interfere with the production of red blood cells and platelets.
- Chronic lymphocytic leukemia (CLL) most often occurs in people over 55 years of age. It is the most common type of leukemia overall, and occurs about twice as often in men as in women. It develops at a slower rate than ALL. Gradually, leukemic cells outnumber the normal-functioning cells in certain tissues in the body, including the bone marrow where other blood cells are made.
- Acute myeloid leukemia (AML) causes uncontrolled production of another type of white blood cell called myelocytes. This causes an overgrowth of their immature cells called myeloblasts. This interferes with the levels of functioning red blood cells, platelets, and normal white blood cells. AML is the most common form of acute leukemia in adults.
- Chronic myelogenous leukemia (CML) occurs more slowly than AML and has less effect on the development of other cell types. Chances of getting CML are very low for children but increase with age. CML is associated with the Philadelphia chromosome.