How Is Acute Myeloid Leukemia Classified?

For most types of cancer, determining the stage (extent) of the cancer is very important. The stage is based on the size of the tumor and how far the cancer has spread. This can be helpful in predicting a person’s outlook and deciding on treatment.

Acute myeloid leukemia (AML), on the other hand, does not usually form tumors. It generally is in all of the bone marrow in the body and, in some cases, has spread to other organs, such as the liver and spleen. Therefore AML is not staged like most other cancers. The outlook for a person with AML depends instead on other information, such as the subtype of AML (determined by lab tests), the patient’s age, and other lab test results.

Knowing the subtype of AML can be very important, as it sometimes affects both a patient’s outlook and the best treatment. For example, the acute promyelocytic leukemia (APL) subtype is often treated using drugs that are different from those used for other subtypes of AML.

Two of the main systems that have been used to classify AML into subtypes are the French-American-British (FAB) classification and the newer World Health Organization (WHO) classification.

The French-American-British (FAB) classification of AML


    FAB subtype



    Undifferentiated acute myeloblastic leukemia


    Acute myeloblastic leukemia with minimal maturation


    Acute myeloblastic leukemia with maturation


    Acute promyelocytic leukemia (APL)


    Acute myelomonocytic leukemia

    M4 eos

    Acute myelomonocytic leukemia with eosinophilia


    Acute monocytic leukemia


    Acute erythroid leukemia


    Acute megakaryoblastic leukemia

Subtypes M0 through M5 all start in immature forms of white blood cells. M6 AML starts in very immature forms of red blood cells, while M7 AML starts in immature forms of cells that make platelets.

World Health Organization (WHO) classification of AML

The FAB classification system is useful and is still commonly used to group AML into subtypes. But it doesn’t take into account many of the factors that are now known to affect prognosis (outlook). The World Health Organization (WHO) has developed a newer system that includes some of these factors to try to better classify AML.

The WHO system divides AML into several groups:

AML with certain genetic abnormalities

  • AML with a translocation between chromosomes 8 and 21
  • AML with a translocation or inversion in chromosome 16
  • AML with a translocation between chromosomes 9 and 11
  • AML with a translocation between chromosomes 6 and 9
  • AML with a translocation or inversion in chromosome 3

AML with myelodysplasia-related changes

AML related to previous chemotherapy or radiation


  • AML with minimal differentiation (M0)
  • AML without maturation (M1)
  • AML with maturation (M2)
  • Acute myelomonocytic leukemia (M4)
  • Acute monocytic leukemia (M5)
  • Acute erythroid leukemia (M6)
  • Acute megakaryoblastic leukemia (M7)
  • Acute basophilic leukemia
  • Acute panmyelosis with fibrosis

Myeloid sarcoma (also known as granulocytic sarcoma or chloroma)

Myeloid proliferations related to Down syndrome


Prognostic factors for acute myeloid leukemia

In recent years, research has focused on why some patients have a better chance to be cured than others. Differences among patients (or their leukemias) that affect response to treatment are called prognostic factors. Prognostic factors help doctors decide if people with a certain type of AML should get more or less treatment. Some of these include:

Chromosome abnormalities

AML cells can have many kinds of chromosome changes, some of which can affect a person’s prognosis. Those listed below are some of the most common, but there are many others. Not all patients have these abnormalities. Patients without any of these usually have an outlook that is between favorable and unfavorable.

Favorable abnormalities:


Unfavorable abnormalities:

  • Translocation or inversion of chromosome 3
  • Translocation between chromosomes 6 and 9
  • Translocation between chromosomes 9 and 22
  • Abnormalities of chromosome 11 (at the spot q23)

Gene mutations

People whose leukemia cells have certain gene mutations may have a better or worse outlook.




Markers on the leukemia cells

If the leukemia cells have the CD34 protein and/or the P-glycoprotein (MDR1 gene product) on their surface, it is linked to a worse outcome.


Older patients (over 60) generally don’t do as well as younger patients. Some of this may be because they are more likely to have unfavorable chromosome abnormalities. Older patients sometimes also have other medical conditions that can make it harder to treat them with more intense chemotherapy regimens.

White blood cell count


Prior blood disorder leading to AML


Treatment-related AML




Leukemia cells in the central nervous system

Leukemia that has spread to the area around the brain and spinal cord can be hard to treat, since most chemotherapy drugs can’t reach that area.

Status of acute myeloid leukemia after treatment

Not surprisingly, how well (and how quickly) the leukemia responds to treatment also affects long-term prognosis. Better responses have been linked with better long-term outcomes.


Minimal residual disease is a term used after treatment when leukemia cells can’t be found in the bone marrow using standard tests (such as looking at cells under a microscope), but more sensitive tests (such as flow cytometry or PCR) find evidence that there are still leukemia cells in the bone marrow.

Active disease means that either there is evidence that the leukemia is still present during treatment or that the disease has come back after treatment (relapsed). For a patient to have relapsed, they must have more than 5% blast cells in their bone marrow.

The American Cancer Society medical and editorial content team

