What is leukemia?
Leukemia is a type of cancer. Cancer is a group of more than 100 diseases that have two important things in common. One is that certain cells in the body become abnormal. Another is that the body keeps producing large numbers of these abnormal cells. Leukemia is cancer of the blood cells. To understand leukemia, it is helpful to know about normal blood cells and what happens to them when leukemia develops.
Normal blood cells
The blood is made up of fluid called plasma and three types of cells. Each type has special functions. White blood cells (also called WBCs or leukocytes) help the body fight infections and other diseases. Red blood cells (also called RBCs or erythrocytes) carry oxygen from the lungs to the body's tissues and take carbon dioxide from the tissues back to the lungs. The red blood cells give blood its color. Platelets (also called thrombocytes) help form blood clots that control bleeding.
Blood cells are formed in the bone marrow, the soft, spongy center of bones. New (immature) blood cells are called blasts . Some blasts stay in the marrow to mature. Some travel to other parts of the body to mature. Normally, blood cells are produced in an orderly, controlled way, as the body needs them. This process helps keep us healthy.
When leukemia develops, the body produces large numbers of abnormal blood cells. In most types of leukemia, the abnormal cells are white blood cells. The leukemia cells usually look different from normal blood cells, and they do not function properly.
Types of leukemia
There are several types of leukemia. They are grouped in two ways. One way is by how quickly the disease develops and gets worse. The other way is by the type of blood cell that is affected. Leukemia is either acute or chronic.
In acute leukemia, the abnormal blood cells are blasts. They remain very immature and cannot carry out their normal functions. The number of blasts increases rapidly, and the disease gets worse quickly.
In chronic leukemia, some blast cells are present. In general, however, these cells are more mature and can carry out some of their normal functions. Also, the number of blasts increases less rapidly than in acute leukemia. As a result, chronic leukemia gets worse gradually.
Lymphocytic and myeliod leukemias
Leukemia can arise in either of the two main types of white blood cells-lymphoid cells or myeloid cells. When leukemia affects lymphoid cells, it is called lymphocytic leukemia . When myeloid cells are affected, the disease is called myeloid or myelogenous leukemia . These are the most common types of leukemia:
- Acute lymphocytic leukemia (ALL) is the most common type of leukemia in young children. This disease also affects adults, especially those age 65 and older.
- Acute myeloid leukemia (AML) occurs in both adults and children. This type of leukemia is sometimes called acute nonlymphocytic leukemia (ANLL).
- Chronic lymphocytic leukemia (CLL) most often affects adults over the age of 55. It sometimes occurs in younger adults, but it almost never affects children.
- Chronic myeloid leukemia (CML) occurs mainly in adults. A very small number of children also develop this disease.
Hairy cell leukemia is an uncommon type of chronic leukemia. There are a number of other uncommon types of leukemia.
The National Cancer Institute, May 2001
Last reviewed May 2001 by
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