Bone Marrow &
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 individuals that the blood actually has a whitish tinge.
Under normal circumstances, the blood-forming, or hematopoietic, cells of the bone marrow make leukocytes to defend the body against infectious organisms such as viruses and bacteria. But 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.
The leukemic cells accumulate and lessen the production of oxygen-carrying red blood cells (eythrocytes), blood-clotting cells (platelets), and normal leukocytes. If untreated, the surplus 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 four types are the most common:
Acute leukemias usually develop suddenly, whereas some chronic varieties may exist for years before they are diagnosed.
Leukemia Facts & Figures
Leukemia often is thought to be a childhood disease. In fact, leukemia strikes 10 times as many adults as children. The American Cancer Society (ACS) predicts that about 30,200 new leukemia cases - 27,900 adults and 2,300 children - will be diagnosed in the United States during 1999. Acute myelogenous leukemia (AML) is the most frequently reported form of leukemia in adults, and approximately 10,100 new cases are anticipated in 1999.
About 41% of the 30,200 latest cases will have chronic leukemia - an estimated 7,800 chronic lymphocytic leukemia (CLL) cases and 4,500 chronic myelogenous leukemia (CML) cases. In addition, hairy cell leukemia (HCL), a slow-growing lymphocytic cancer, will account for about 604 cases (2% of all leukemias). Sadly, it is estimated that approximately 22,100 American adults and children will die of leukemia in 1999.
Acute myelogenous leukemia (AML) is the most common adult form of leukemia, affecting nearly 5 in every 100,000 men each year.
Chronic leukemia, like many other cancers, is a "disease of old age." The average age of individuals with chronic lymphocytic leukemia (CLL) is roughly 70 years, and the average age of chronic myelogenous leukemia (CML) patients is 40 to 50 years. By contrast, acute lymphocytic leukemia (ALL) is largely a pediatric disease, usually appearing in children who are under 10 years of age.
In general, leukemia affects more men than women throughout the world, although the male:female ratio is highest in CLL patients in Western countries.