The classification system for acute myelogenous leukemia (AML), proposed by the World Health Organization (WHO), is based on the cytogenetic structure and arrangement of chromosomes in leukemic cells.
World Health Organization Classification
WHO classifies AML into four principal types.
1) AML with characteristic genetic abnormalities
- AML with inversions in chromosome 16
- AML with translocations between chromosomes 15 and 17
- AML with translocations between chromosomes 8 and 21
These types of AML are more common in younger patients. Patients with the 15:17 translocation are said to have acute promyelocytic leukemia (APL). Treatment for APL differs from that for other types of AML.
2) AML arising from a previous hematologic disorder
About one-third of AML patients—particularly those over the age of 65—have abnormalities in blood counts for months before the diagnosis of AML. These patients often do poorly with standard therapy and consequently may be candidates for clinical studies of new therapies.
3) Therapy-related AML
About a quarter of AML patients have received chemotherapy for another malignancy, such as breast cancer or lymphoma, usually 5 to 10 years before development of AML but occasionally less than 2 years before.
4) Patients with AML not falling into one of the above categories
These patients are classified according to how their leukemic cells appear under a microscope. However, the prognostic and biologic significance of such microscopic appearance is uncertain, and classification based the appearance of leukemic cells will almost certainly be replaced by classification based on their molecular features.