Acute myeloid leukemia (AML) is the most common type of leukemia diagnosed in adults. The American Cancer Society estimates that 20,050 people will receive a diagnosis of AML in 2022.

AML goes by many other names, such as:

  • acute granulocytic leukemia
  • acute nonlymphocytic leukemia
  • acute myelocytic leukemia
  • acute myelogenous leukemia

Doctors divide AML into subtypes based on the characteristics of cancer cells. Identifying which subtype you have can be very important for determining the best treatment and predicting your outlook.

Read on to learn more about the subtypes of AML and the different systems used to classify them.

About leukemia

Leukemia is a group of cancers that develop in blood cells. It’s classified based on how fast it develops and what type of cells are affected.

“Acute” leukemia means that the cancer is expected to develop quickly and requires prompt treatment. “Myeloid” leukemia means that it develops in myeloid stem cells that become red blood cells, platelets, and some types of white blood cells.

Doctors divide most types of cancer into stages based on the size of the tumor and how far the cancer has spread. However, unlike most cancers, AML usually does not cause tumors. Doctors divide AML into subtypes instead of stages to predict the outlook and guide treatment.

Two primary classification systems have been used to categorize AML:

  1. French-American-British (FAB) system. A group of researchers created the FAB system in the 1970s. This system classifies AML into the subtypes M0 to M7 mostly based on how cancer cells look under a microscope.
  2. World Health Organization (WHO) system. The WHO system is now the main system used to classify AML. It considers more factors known to influence someone’s outlook, such as gene mutations or “abnormalities” in chromosomes.

Diagnosing AML subtypes

Diagnosing AML starts with a physical exam and a review of your medical history. If your doctor suspects a blood cancer, they’ll order blood tests to help look for signs of leukemia. These often include:

  • a complete blood count to identify an atypically high white blood cell count or low red blood cell and platelet count
  • a peripheral blood smear to look for atypical characteristics in the size and shape of your blood cells

To confirm an AML diagnosis, doctors take a small sample of your bone marrow for lab analysis. This sample is usually taken from your hip bone.

Cells in your sample will be analyzed in a lab to distinguish your cancer from other types of leukemia and to look for certain genetic mutations. These tests include:

  • immunophenotyping (flow cytometry)
  • cytogenetic analysis (karyotyping)
  • polymerase chain reaction (PCR)
  • DNA sequencing

The FAB system classifies AML based on the type of cells the cancer develops in and how mature these cells are.

The subtypes in the FAB system are:

SubtypeCells where cancer startsName
M0immature white blood cellsundifferentiated acute myeloblastic leukemia
M1immature white blood cellsacute myeloblastic leukemia with minimal maturation
M2immature white blood cellsacute myeloblastic leukemia with maturation
M3immature white blood cellsacute promyelocytic leukemia (APL)
M4immature white blood cellsacute myelomonocytic leukemia
M4 eosimmature white blood cellsacute myelomonocytic leukemia with eosinophilia
M5immature white blood cellsacute monocytic leukemia
M6very immature red blood cellsacute erythroid leukemia
M7immature plateletsacute megakaryoblastic leukemia

The WHO system is now the main system used to classify AML. The WHO International Classification of Diseases 11 (ICD-11), which came into effect in January 2022, lists the following subtypes:

  • AML with recurrent genetic abnormalities. These subtypes are associated with certain gene changes and are further categorized as:
    • AML (megakaryoblastic) with a translocation between chromosomes 1 and 22
    • AML with a translocation or inversion in chromosome 3
    • AML with a translocation between chromosomes 6 and 9
    • AML with a translocation between chromosomes 8 and 21
    • AML with a translocation between chromosomes 9 and 11
    • AML with a translocation or inversion in chromosome 16
    • APL (acute promyelocytic leukemia) with the PML-RARA fusion gene
    • AML with the mutated NPM1 gene
    • AML with two mutations of the CEBPA gene
    • AML with the BCR-ABL1 (BCR-ABL) fusion gene (it’s not clear yet if this is a unique group)
    • AML with mutated RUNX1 gene (it’s not clear yet if this is a unique group)
  • AML with myelodysplasia-related changes
  • therapy-related myeloid neoplasms
  • myeloid sarcoma
  • myeloid proliferations related to Down syndrome
  • blastic plasmacytoid dendritic cell neoplasm
  • AML, not otherwise classified. These subtypes of AML do not fall into one of the other categories. They closely follow the FAB classification and include:
    • acute basophilic leukemia
    • acute panmyelosis with fibrosis
    • AML with minimal differentiation (M0)
    • AML without maturation (M1)
    • AML with maturation (M2)
    • acute myelomonocytic leukemia (M4)
    • acute monoblastic/monocytic leukemia (M5)
    • pure erythroid leukemia (M6)
    • acute megakaryoblastic leukemia (M7)

A translocation is when part of a chromosome switches with another.

Doctors use AML subtypes to help guide treatment decisions. The main treatment for most types of AML is chemotherapy. Certain types of AML like promyelocytic leukemia are treated with different drugs than other subtypes.

When determining the best treatment, doctors also consider other factors like:

  • your age and overall health
  • specific gene mutations
  • chromosome irregularities
  • markers on leukemia cells, such as the protein CD34
  • blood cell count

Knowing your AML subtype can be very important for determining your outlook. Certain subtypes are linked to more favorable or less favorable outcomes.

For instance, AML with myelodysplasia-related changes and therapy-related myeloid neoplasms tend to have poor outlooks compared to other types of AML.

Many other factors also play a role in determining your outlook and how intensive your treatment should be. Doctors call these “prognostic factors.”

Chromosome abnormalities

Atypical characteristics in the chromosomes of AML cells can also influence your outlook. Changes associated with a favorable outlook include:

  • translocation between chromosomes 8 and 21
  • translocation or inversion of chromosome 16
  • translocation between chromosomes 15 and 17

Atypical characteristics associated with an unfavorable outlook include:

  • loss of one of two copies of a chromosome
  • loss of part of chromosome 5 or 7
  • abnormalities of chromosome 11
  • translocation between chromosomes 6 and 9
  • translocation or inversion of chromosome 3
  • translocation between chromosomes 9 and 22
  • changes involving three or more chromosomes

Other factors that affect outlook

Other factors that affect your outlook include the following:

FactorNotes
gene mutationsSome mutations like the FLT3 geneare associated with a less favorable outlook.
ageYounger people tend to have a better outlook than older people.
white blood cell countA white blood cell count over 100,000/mm3at the time of diagnosis is associated with a less favorable outlook.
prior blood disorderHaving a prior blood disorder is associated with a less favorable outlook.
AML after treatment for another cancerAML that develops after previous cancer treatment is associated with a less favorable outlook.
infectionHaving a blood infection at the time of diagnosis is associated with a less favorable outlook.
involvement of your nervous systemLeukemia cells in your brain or spinal cord are associated with a less favorable outlook.

AML is a type of cancer that develops in immature blood cells. It’s divided into subtypes depending on how the cells look under a microscope and other factors, like the presence of certain chromosome abnormalities or gene mutations.

Knowing which subtype you have can be important for determining the best treatment options and your outlook. Your doctor can explain which subtype you have and how it influences your treatment plan.