Acute Myelogenous Leukemia Subtypes

by Myrrh Hector

for About.com

Updated December 04, 2008

About.com Health's Disease and Condition content is reviewed by the Medical Review Board

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Leukemia Types

Because acute myelogenous leukemia (also called acute myeloid leukemia) doesn't usually develop solid tumors, AML cases are divided into specific subtypes instead of numbered stages. Two systems currently exist for classifying AML into subtypes, the French-American-British system and the World Health Organization system.

The French-American-British (FAB) Classification System:

Developed by a group of French, American, and British doctors in the 1970's, the FAB system is based on examination of the leukemic cells under a microscope. The subtypes are divided according to the type of [cell from which the leukemia cells developed and their degree of maturity. These eight subtypes are:

M0: Undifferentiated Acute Myeloblastic Leukemia. M0 leukemia cells show no signs of maturation, or the development of distinguishing cell characteristics. This type of leukemia accounts for 5% of adult leukemia patients, and is associated with a prognosis that is worse than the average for AML.

M1: Acute Myeloblastic Leukemia with Minimal Maturation. The leukemia cells show minimal signs of development and granulocytic differentiation. 15% of adult AML patients are diagnosed with this subtype, which is associated with an average prognosis.

M2: Acute Myeloblastic Leukemia with Maturation. Leukemic cell differentiation is at or beyond the early granulocyte, or promyelocyte, stage. This type may be linked to a translocation between chromosomes 8 and 21, and accounts for 25% of adult AML cases. The M2 type carries with it a better prognosis than is average for most cases of AML.

M3: Acute Promyelocytic Leukemia. The cellular characteristics of this type of leukemia include nuclei of various shapes and sizes, and most of the abnormal cells observed are early granulocytes that are between the myeloblast and myelocyte stages of development. Ten percent of adult AML patients are diagnosed with this subtype, and the prognosis for these patients is better than for all of the other AML types.

M4: Acute Myelomonocytic Leukemia. In this type of leukemia, the proportion of immature monocytes (promonocytes) and monocytes to all blood cells with nuclei is greater than 20%. Approximately 20% of adult AML patients are diagnosed with this type, and their prognosis is similiar to the average prognosis for all AML cases.

M4 eos: Acute Myelomonocytic Leukemia with Eosinophilia. In addition to a higher than normal proportion of monocytes and promonocytes, this M4 variant also involves the presence of abnormal eosinophils in the bone marrow. This type makes up 5% of adult AML cases, and the prognosis for patients with this type of AML is better than average.

M5: Monocytic Leukemia. Poorly differentiated monocytes with DNA that appears lacy characterizes one of the two M5 types of AML.

The other is evidenced by large numbers of monocytes at all different stages of differentiation. Approximately 10% of adult AML patients are diagnosed with monocytic leukemia, and the prognosis for this patients is average when compared with that of all adult patients with AML.

M6: Acute Erythroid Leukemia. In this type of leukemia, over half of the cells with nuclei in the bone marrow are abnormal erythroblasts (red blood cell-forming cells).

M7: Acute Megakaryoblastic Leukemia. This type of leukemia can sometimes be identified by the presence of fibrosis, or fibrous tissue deposits, in the bone marrow. The leukemic cells in this type of leukemia look like lymphocyte-forming cells (lymphoblasts) or immature megakaryocytes.

World Health Organization Classification of Acute Myelogenous Leukemia:

While the FAB system is still the most commonly used, some doctors now refer to the World Health Organization (WHO) system of classification when diagnosing cases of AML and planning the most appropriate treatment. WHO Classification divides AML into broader groups based on factors such as genetic abnormalities and the presence of other leukemia-related blood disorders like myelodysplastic syndrome. These groups are as follows:

AML with Recurrent Genetic Abnormalities

AML with translocation of certain genes between chromosomes 8 and 21
AML with translocation of certain genes between chromosomes 15 and 17
AML with inversion or translocation of certain genes on chromosome 16
AML with abnormalities of chromosome 11
Acute Promyelocytic Leukemia

AML with multilineage dysplasia (leukemia in which more than one abnormal myeloid cell type is involved)

With prior myelodysplastic syndrome
Without prior myelodysplastic syndrome

AML with Myelodysplastic Syndrome, Therapy-Related

Alkylating agent-related - alkylating agents are a certain type of drug used in chemotherapy for various cancers. Examples would include drugs like altretamine.
Epipodophyllotoxin-related - epipodophyllotoxins are also used in chemotherapy
Other Types

AML Not Otherwise Categorized

AML minimally differentiated (MO)
AML without maturation (M1)
AML with maturation (M2)
Acute myelomonocytic leukemia (M4)
Acute monocytic leukemia (M5)
Acute erythroid leukemia (M6)
Acute megakaryocytic leukemia (M7)
Acute basophilic leukemia
Acute panmyelosis with myelofibrosis

_Sources:

"How Is Acute Myeloid Leukemia (AML) Classified?" American Cancer Society. Accessed: 30 November 2008. http://www.cancer.org/docroot/CRI/content/CRI_2_4_3x_How_Is_Acute_Myeloid_Leukemia_AML_Classified.asp.

"Acute Myelogenous Leukemia: Subtypes of AML." Leukemia and Lymphoma Society. Accessed: 30 November 2008.http://www.leukemia-lymphoma.org/all_page.adp?item_id=8459#subtypes.

Harris, Nancy Lee, M.D. et al. "The World Health Organization Classification of Hematological Malignancies Report of the Clinical Advisory Committee Meeting, Airlie House, Virginia, November 1997." Modern Pathology.Accessed: 30 November 2008. http://www.nature.com/modpathol/journal/v13/n2/full/3880035a.html.