Leukemia

Leukemia is cancer that starts in the tissue that forms blood cells (called bone marrow). Blood cells develop from stem cells in the bone marrow. These stem cells mature into specialized blood cells.

• White blood cells help fight infection. There are several types of white blood cells.
• Red blood cells carry oxygen to tissues throughout the body.
• Platelets help form blood clots that control bleeding.

Different types of white blood cells develop in the bone marrow. A stem cell matures into either a myeloid stem cell or a lymphoid stem cell.

• A myeloid stem cell matures into a myeloid blast. The blast can form a red blood cell, platelets, or one of several types of white blood cells.
• A lymphoid stem cell matures into a lymphoid blast. The blast can form one of several types of white blood cells, such as B cells or T cells.

Leukemia occurs when the bone marrow makes large numbers of abnormal white blood cells. As the number of abnormal cells increases in the blood and bone marrow, there is less room for healthy cells.

Types of Leukemia

The types of leukemia can be grouped based on how quickly the disease develops and worsens. Leukemia is either chronic (develops slowly) or acute (develops quickly):

• Chronic leukemia: There may not be any symptoms at first, because the leukemia cells can still do some work of normal white blood cells early in the disease. Doctors often find chronic leukemia during a routine checkup before there are any symptoms.
• Acute leukemia: The leukemia cells can't do any work of normal white blood cells. The number of leukemia cells increases rapidly, and the disease usually worsens quickly.

There are four common types of leukemia:

• Chronic lymphocytic leukemia (CLL): CLL affects lymphocytes (cells of the lymphatic system) and usually grows slowly. It accounts for more than 15,000 new cases of leukemia each year. It is most often diagnosed in people over age 55. It is very rare in children.
• Chronic myeloid leukemia (CML): CML affects myeloid cells and usually grows slowly at first. It accounts for nearly 5,000 new cases of leukemia each year. It mainly affects adults.
• Acute lymphocytic leukemia (ALL): ALL affects lymphocytes and grows quickly. It accounts for more than 5,000 new cases of leukemia each year. ALL is the most common type of leukemia in children. It also affects adults.
• Acute myeloid leukemia (AML): AML affects myeloid cells and grows quickly. It accounts for more than 13,000 new cases of leukemia each year. It occurs in both adults and children.