Leukemia and Blood Cells

Leukemia is cancer of the blood cells. To better understand leukemia, it is helpful to know about normal blood cells and what happens to them when leukemia develops.

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; others 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: by how quickly the disease develops and gets worse and by the type of blood cell affected.

Leukemia is either acute or chronic. In acute leukemia, the abnormal blood cells are blasts that 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, but in general, 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.

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.

There are other, less common types of leukemia, including hairy cell leukemia.

Last Updated: 5/1/2003
The Johns Hopkins University 1996-2003.  All rights reserved.  This information is not intended to provide advice on personal medical matters, nor is it intended to be a substitute for consultation.