Leukemia is an abnormal rise in the number of white blood cells. The white blood cells crowd out other blood cell elements such as red blood cells and platelets. The elevated white blood cells are immature and do not function properly.
Leukemia -- the term derives from the Greek words for "white" and "blood" -- is often considered a disease of children, yet it actually affects far more adults. It is more common in men than women and in Caucasians than African-Americans. There will be more than 52,000 new patients diagnosed with all forms of leukemia in the United States in 2014 with about 24,000 deaths.
Blood has three types of cells: white blood cells that fight infection, red blood cells that carry oxygen, and platelets that help blood to clot, all suspended in its liquid plasma. Every day, hundreds of billions of new blood cells are produced in the bone marrow -- most of them red cells. In people with leukemia, however, the body starts producing more white cells than it needs. Many of the extra white cells do not mature normally, yet they tend to live well beyond their normal life span.
Despite their vast numbers, these leukemia cells are unable to fight infection the way normal white blood cells do. As they accumulate, they interfere with vital organ functions, including the production of healthy blood cells. Eventually, the body does not have enough red blood cells to supply oxygen, enough platelets to ensure proper clotting, or enough normal white blood cells to fight infection. This results in persons with leukemia being anemic as well as increasing their risks of bruising, bleeding, and infection.
Cases of leukemia are classified as acute or chronic. The cells in acute leukemia start multiplying before they develop beyond their immature stage. Chronic leukemia progress more slowly, with the leukemia cells developing to full maturity. Leukemia is further classified according to the type of white blood cell involved, most commonly myeloid or lymphoid. Under a microscope, the two main types of white blood cells are easily distinguishable as myeloid cells contain tiny particles or granules; lymphoid cells usually do not.