Leukemia is a cancer of the blood cells. Leukemia begins when normal blood cells change and grow uncontrollably. Blood cells (including red cells that carry oxygen, white cells that fight infection, and platelets that cause blood to clot) are produced in the bone marrow, the spongy tissue inside the larger bones in the body. Types of leukemia are named after the specific blood cell that becomes cancerous, such as the lymphoid cells (white blood cells of the immune system) or the myeloid cells (cells of the bone marrow which develop into cells which fight bacterial infections). There are four main types of leukemia in adults:
There are other, less common types of leukemia, but they are generally subcategories of one of the four main categories. This section focuses on prolymphocytic leukemia (PLL) and hairy cell leukemia (HCL), both of which are chronic B-cell leukemias. B cells are a specific type of lymphocyte that normally produce antibodies for the immune system.
In PLL, large numbers of immature lymphocytes, or prolymphocytes, are present in the blood. This type of leukemia may occur by itself, together with CLL, or CLL may transform into PLL.
HCL is a slow-growing form of leukemia. It is called “hairy cell” because the abnormal lymphocytes have projections that look like hair when seen under a microscope. As these cells multiply, they accumulate in the bone marrow, blood, and spleen. Because these lymphocytes are abnormal, they do not perform their normal functions in fighting disease and infection, and eventually may crowd out the normal cells. HCL typically responds well to treatment.
Statistics
In 2009, an estimated 44,790 people of all ages (25,630 men and 19,160 women) in the United States will be diagnosed with leukemia. HCL accounts for about 2% of all leukemia cases. An estimated 15,490 people (9,200 men and 6,290 women) in the United States will be diagnosed with CLL. There are no current estimates for PLL.
Cancer statistics should be interpreted with caution. These estimates are based on data from thousands of cases of this type of cancer in the United States, but the actual risk for a particular individual may differ. It is not possible to tell a person how long he or she will live with leukemia.
Statistics adapted from the American Cancer Society's publication, Cancer Facts and Figures 2009.
Find out more about basic cancer terms used in this section.
Last Updated: November 24, 2009
