Overview

Leukemia, a cancer of the blood, is the most common type of cancer in children. The most common type of leukemia in children is acute lymphoblastic leukemia (also called acute lymphocytic leukemia, acute lymphoid leukemia, or ALL). In ALL, the normal cells in a child’s bone marrow are overwhelmed and replaced by abnormal lymphoblasts, which are immature lymphocytes (a type of white blood cell).

Normal lymphocytes fight infections in the body. However, when a child has ALL, the lymphoblasts that fill the bone marrow are abnormal and do not develop into mature cells that can produce the antibodies needed to prevent and treat infection. These abnormal lymphoblasts also crowd out other normal cells in the bone marrow, preventing the production of red cells, many other types of normal white blood cells, and platelets (cells that help blood to clot). If the bone marrow is not functioning correctly, the child may experience the following:

• Anemia occurs when the blood has too few red cells. Anemia can lead to fatigue, irritability, sleepiness, pallor (paleness), shortness of breath, and a rapid heartbeat.
  
  
• Bruising or bleeding from injuries may occur more easily, because the blood cannot clot normally when the platelet count is low.
  
  
• Infection may occur more often if the blood has too few normal white blood cells. Many types of white blood cells are needed (for example, granulocytes, which are often called segmented cells or polys, as well as monocytes and lymphocytes) for normal, healthy functions. 

The leukemic lymphoblasts may also collect in the child’s lymph nodes and cause them to swell. Lymphoblasts may also invade other organs, including the spinal cord, brain, skin, liver, spleen, ovaries (in girls), testicles (in boys), and the spinal fluid.

This section is about ALL that occurs in children, sometimes called pediatric ALL. For information on adult acute lymphocytic leukemia, please visit Leukemia, Acute Lymphocytic (ALL).

Statistics

ALL is the most common type of childhood cancer. In 2009, an estimated 2,655 children, age 0 through 19, in the United States will be diagnosed with ALL. It is most common in younger children, especially children age two through four. The five-year relative survival rate (the percentage of people who survive at least five years after the cancer is detected, excluding those who die from other diseases) for children with ALL is more than 80%.

Cancer survival 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 each year, 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 childhood ALL. Because the survival statistics are measured in five-year intervals, they may not represent advances made in the treatment or diagnosis of this cancer.

Source: American Cancer Society

Find out more about basic cancer terms used in this section.