Overview of Leukemia
Leukemia is a form of cancer that begins in the blood-forming cells of the bone marrow—the soft, inner part of the bones. Leukemia, which literally means "white blood" in Greek, occurs when there is an excess of abnormal white blood cells in the blood. Known as leukocytes, these cells are so plentiful in some patients that the blood actually has a whitish tinge.
Under normal circumstances, the blood-forming (hematopoietic) cells of the bone marrow make leukocytes to defend the body against infectious organisms, such as viruses and bacteria. If some leukocytes are damaged and remain in an immature form, they become poor infection fighters that multiply excessively and do not die off as they should.
These damaged leukemic cells accumulate and lessen the production of oxygen-carrying red blood cells (erythrocytes), blood-clotting cells (platelets), and normal leukocytes. If untreated, these leukemic cells overwhelm the bone marrow, enter the bloodstream, and eventually invade other parts of the body, such as the lymph nodes, spleen, liver, and central nervous system (brain, spinal cord). In this way, the behavior of leukemia is different than that of other cancers, which usually begin in major organs and ultimately spread to the bone marrow.
There are more than a dozen varieties of leukemia, but the following 4 types are the most common:
- Acute myelogenous leukemia (AML)
- Chronic myelogenous leukemia (CML)
- Acute lymphocytic leukemia (ALL)
- Chronic lymphocytic leukemia (CLL)
Acute leukemias usually develop suddenly, whereas some chronic types may exist for years before they are diagnosed.