Childhood Acute Lymphoblastic Leukemia (ALL)

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Childhood acute lymphoblastic leukemia (also called acute lymphocytic leukemia or ALL) is a cancer of the blood and bone marrow. This type of cancer usually gets worse quickly if it is not treated. It is the most common type of cancer in children.

Normally, the bone marrow makes blood stem cells (immature cells) that develop into mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell.

The myeloid stem cell develops into one of three types of mature blood cells:

• Red blood cells that carry oxygen and other materials to all tissues of the body.
• Platelets that help prevent bleeding by causing blood clots to form.
• Granulocytes (white blood cells) that fight infection and disease.

The lymphoid stem cell develops into a lymphoblast cell and then into one of three types of lymphocytes (white blood cells):

• B lymphocytes that make antibodies to help fight infection.
• T lymphocytes that help B lymphocytes make the antibodies that help fight infection.
• Natural killer cells that attack cancer cells and viruses.

Blood cell development. A blood stem cell goes through several steps to become a red blood cell, platelet, or white blood cell.

In ALL, too many stem cells develop into lymphoblasts and do not mature to become lymphocytes. These lymphoblasts are called leukemia cells. The leukemia cells do not work like normal lymphocytes and are not able to fight infection very well. Also, as the number of leukemia cells increases in the blood and bone marrow, there is less room for healthy white blood cells, red blood cells, and platelets. This may lead to infection, anemia, and easy bleeding.

There are subgroups of childhood ALL.

There are different subgroups of ALL based on the following:

• Whether the type of blood cell that is affected looks more like a B lymphocyte or a T lymphocyte.
• The age of the child at diagnosis. For example, whether the child is younger than one year, one year to 10 years old, or older than 10 years (teenager).
• Whether there are certain changes in the chromosomes. Philadelphia chromosome -positive ALL is one type of chromosome change that may occur.