Acute myeloid leukemia (AML)
AML accounts for almost 90% of acute leukemias, and is more commonly seen in adults than children. The marrow or blood contains 20% or more blasts committed to the myeloid series. The French-American-British classification system recognizes eight major types of AML (FAB M0-M7) based on the type of myeloid precursor - neutrophilic, monocytic, erythroid, or megakaryocytic, and degree of differentiation or maturation. The new WHO classification also incorporates genetic information into the diagnosis.
Myeloblasts are uniform in appearance, approximately 25-30 µ in diameter. They have bland, fine chromatin and 1 to 3 prominent nucleoli. The scanty blue cytoplasm is typically agranular.
Blasts accumulate in the marrow, displacing normal progenitors, and so ultimately replace the marrow with immature, neoplastic, nonfunctional cells. Untreated, AML is lethal within weeks to months.
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