Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

Acute lymphocytic leukemia (ALL) is a cancer of the body's blood-making system. (It is also known as acute lymphoblastic leukemia and acute lymphoid leukemia.) The word "acute" refers to the fact that the disease can progress quickly. "Lymphocytic" means that the cancer develops from lymphocytes, a type of white blood cell.

Bone marrow, the soft inner part of bones, makes cells that circulate in the blood. They include white blood cells, red blood cells, and platelets. The two major types of white blood cells are myeloid cells and lymphoid cells. Lymphocytes form from lymphoid cells.

Normally, the bone marrow makes three types of infection-fighting lymphocytes:

  • B lymphocytes These cells make antibodies to help protect the body from germs.

  • T lymphocytes These cells can destroy virus-infected cells, foreign cells, and cancer cells. They also help make antibodies.

  • Natural killer cells These cells can also kill cancer cells and viruses.

In ALL, the bone marrow makes too many immature lymphocytes. These lymphocytes, called blasts, contain abnormal genetic material. They cannot fight infections as well as normal cells. In addition, because these lymphocytes multiply quickly, they crowd out healthy white blood cells, red blood cells, and platelets in the blood and bone marrow. This may lead to infection, anemia, and easy bleeding.

ALL typically invades the blood quickly. It can involve other parts of the body, such as the lymph nodes, liver, spleen, brain and spinal cord (central nervous system), and testicles (testes).

Although it is rare, ALL is the most common cancer in children. It can affect children of any age, but most are diagnosed between 2 and 4 years old.

A few factors may increase a child's risk of developing ALL. These include

  • having a sibling with leukemia

  • being white

  • being male

  • exposure to x-rays before birth

  • exposure to radiation

  • past treatment with chemotherapy or other drugs that weaken the immune system

  • having certain inherited disorders, such as Down syndrome

  • having a specific genetic change (mutation).

Having one or more of these risk factors does not mean your child will develop ALL. Many children with the disease have no risk factors.

ALL has several subtypes. Subtypes depend on

  • whether the cancerous cells formed from B lymphocytes or T lymphocytes

  • your child's age

  • whether the cells have certain changes in their genetic material.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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