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The World Health Organization (WHO) classification system is the most commonly used method to split acute lymphoblastic leukemia into distinct subtypes.

The French, American, and British (FAB) is another, older system, but it has mostly been replaced by laboratory tests, which allow more accurate classification.1


Based on the type of white blood cell (lymphocyte) affected, three main subtypes can be found:

B-cell acute lymphoblastic leukemia (or B-acute lymphoblastic leukemia), most common type (80% of cases)

  • Most B-acute lymphoblastic leukemias stem from abnormal immature (pre) B cells.
  • Some B-acute lymphoblastic leukemias develop from malignant mature B cells. You may also hear it called Burkitt type acute lymphoblastic leukemia, as it is similar to another type of cancer called Burkitt lymphoma.2

T-cell acute lymphoblastic leukemia (or T-acute lymphoblastic leukemia)(20% of cases)

  • More frequent in young adults and in men.

Mixed phenotype acute leukemia

A very rare form of leukemia where the leukemic cells exhibit both lymphoid and myeloid features. You may also hear this called acute biphenotypic leukemia or acute bilineal leukemia.

Further classification

Leukemia subtypes can be further categorized according to genetic abnormalities into around 25 different subtypes. 

Philadelphia-positive acute lymphoblastic leukemia

One well-known change that occurs in acute lymphoblastic leukemia is formation of the Philadelphia chromosome, which is caused by the exchange of genetic material between chromosomes 9 and 22 in the leukemic cells. If this change is present, the leukemia is described as being Philadelphia positive.

Around 20−30% of adult patients with B-acute lymphoblastic leukemia have this change.2 This change does not affect non-cancer cells and is not inherited or passed on to your children. The Philadelphia chromosome confers a sensitivity to drugs called tyrosine kinase inhibitors, which are used to treat Philadelphia-positive acute lymphoblastic leukemia. If you or your child has Philadelphia-positive acute lymphoblastic leukemia, you may be given a drug called imatinib alongside other standard antileukemic drugs. You can read more about this and other therapies on the treatment page.


1. American Cancer Society. Acute lymphocytic leukemia (ALL) subtypes and prognostic factors. Published Oct 17, 2018. Accessed Mar 29, 2021.

2. Cancer Research UK. Types. Published May 10, 2018. Accessed Mar 29, 2021.

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What is acute lymphoblastic leukemia?Causes & symptomsDiagnosisTypesTreatmentPrognosisRemissionRelapse

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