Understanding the Morphological Aspects of Acute Myeloid Leukemia (AML)
Acute Myeloid Leukemia (AML) is a type of cancer that affects the blood and bone marrow, leading to the production of abnormal myeloid cells. This article provides an overview of the two systems used to classify AML: the French-American-British (FAB) system and the World Health Organization (WHO) system.
The FAB system, developed earlier, is based primarily on the morphological and cytochemical features of leukemic cells. It categorizes AML into eight subtypes (M0 through M7) according to the maturation stage and lineage involvement of myeloid cells.
On the other hand, the WHO classification, updated in 2022, incorporates genetic, molecular, and clinical data in addition to morphology. It classifies AML into categories based on defining genetic abnormalities, morphological differentiation, myelodysplasia-related changes, secondary AML, and specific subtypes.
While the FAB system is purely morphology-driven, the WHO classification offers a genetically informed, multidimensional framework that includes but extends beyond morphology. This allows for more precise diagnosis and risk stratification of AML.
Both systems recognise the importance of morphological assessment of leukemic blasts as a foundation for AML classification. To diagnose AML, doctors typically request samples of blood and bone marrow. A specialist called a pathologist looks at the cells under a microscope to determine whether AML is present, and if so, the disease's subtype. This involves assessing the cancerous cells' size, shape, maturity, and the percentage of these cells in the sample. Additional lab tests may be ordered to identify or confirm the AML subtype, including cytochemistry, flow cytometry and immunohistochemistry, and chromosome tests.
In some cases, chromosomal abnormalities can affect the outlook for someone with AML. Translocations between certain chromosomes, such as those between chromosomes 8 and 21, 16, 15 and 17, and 6 and 9, are associated with a better response to treatment and a more favorable outlook. Conversely, the loss of part of chromosomes 5 or 7, changes involving three or more chromosomes, and abnormalities in chromosome 11 are associated with a less favorable response to treatment and overall outlook.
Genetic mutations within leukemia cells can also impact the outlook for someone with AML. People whose AML involves a mutation in the FLT3 gene tend to have a less favorable outlook, but new drugs targeting this type of mutation may lead to better outcomes. People whose AML involves a mutation in either the CEBPA or NPM1 genes tend to have a more favorable outlook. However, a 2020 study suggests that people with both CEBPA and FLT3 gene mutations tend to have a less favorable outlook.
In conclusion, understanding the FAB and WHO classification systems for AML is crucial for accurate diagnosis and effective treatment. The WHO classification, with its comprehensive approach, offers a more precise and personalized approach to AML diagnosis and risk stratification.
- Acute Myeloid Leukemia (AML) is a type of cancer that affects the blood and bone marrow, leading to the production of abnormal myeloid cells.
- The FAB system, an earlier classification system, categorizes AML into eight subtypes based on the morphological and cytochemical features of leukemic cells.
- The World Health Organization (WHO) classification, updated in 2022, incorporates genetic, molecular, and clinical data in addition to morphology to classify AML.
- Certain genetic mutations within leukemia cells, such as those involving the FLT3, CEBPA, or NPM1 genes, can impact the outlook for someone with AML, with some mutations leading to a more favorable or less favorable response to treatment.
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