Leukemia is a general term for cancer of the blood or bone marrow characterized by an abnormal production of blood cells. It is divided into the following four types:
- acute myelogenous leukemia (AML)
- acute lymphocytic leukemia (ALL)
- chronic myelogenous leukemia (CML)
- chronic lymphocytic leukemia (CLL)
With acute leukemia (AML and ALL) immature blood cells in the bone marrow crowd out normal cells. These nonfunctional cells spill over into the blood stream, and spread to other organs in the body. Acute leukemia is the most commonly found leukemia in children. Acute leukemia progresses very rapidly and requires immediate treatment.
Chronic leukemia (CML and CLL) relatively mature, but abnormal, blood cells multiply excessively over a period or months or years. The number of red cells is generally less than normal, causing anemia. The number of white cells can be much higher than normal. Chronic leukemia occurs most often in older people.
Both acute and chronic leukemias are further subdivided according to what kind of blood cell is affected. All leukemias begin with a leukemic change to a cell in the bone marrow. The cancerous cell multiplies and survives better than normal cells and eventually crowds out the normal cells.
In lymphocytic leukemias (ALL and CLL), the cancerous change occurs in a type of marrow cell that forms lymphocytes, a type of white blood cell that is part of the immune system.
In myelogenous leukemias (AML and CML), the change occurs in a type of marrow cell that forms red blood cells, other white blood cells, and platelets.