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What is acute lymphoblastic leukemia?

Although acute lymphoblastic leukemia is a rare type of leukemia, it is the most common leukemia among children.1 It also affects adults, who comprise 4 out of every 10 cases of acute lymphoblastic leukemia.2 The risk of developing acute lymphoblastic leukemia is highest when under 5 years old or when over 50 years old.2 

Acute lymphoblastic leukemia usually develops quickly over the course of days or weeks and requires rapid treatment. To understand which cells are affected in acute lymphoblastic leukemia, it helps to look at blood composition.

Blood is broadly made up of 4 components:

  1. Red blood cells that carry oxygen and give blood its distinctive color.
  2. White blood cells that fight infection.
  3. Platelets, which are small cells involved in clotting and prevention of excessive bleeding.
  4. Plasma, the straw-colored fluid in which blood cells are suspended.

Under normal conditions, these components exist in relatively stable amounts in relation to each other. Acute lymphoblastic leukemia is a disease in which the number of white blood cells is no longer controlled correctly. White blood cells are produced more rapidly than normal within the bone marrow and are released before they are fully mature (these cells are known as lymphoblasts). This means that although there are more white blood cells in the blood, they do not function correctly.

The overproduction of white blood cells reduces the amount of red blood cells and platelets that are produced, and this causes many of the symptoms of acute lymphoblastic leukemia.


1. Cancer Research UK. What is acute lymphoblastic leukaemia (ALL)? Published May 14, 2018. Accessed Mar 22, 2021.

2. American Cancer Society. Key statistics for acute lymphocytic leukemia (ALL). Published Jan 12, 2021. Accessed Mar 22, 2021.

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What is acute lymphoblastic leukemia?Causes & symptomsDiagnosisTypesTreatmentPrognosisRemissionRelapse

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