Auer rods in mature granulocytes: a unique morphologic feature of acute myelogenous leukemia with maturation.

The authors observed Auer rods in mature neutrophils, bands, and metamyelocytes in two children with AML with maturation (FAB M2). In order to determine if this rare finding was characteristic of AML M2, the authors reviewed the bone marrows and peripheral blood smears of 50 children with AML M2 and 50 children with other AML subtypes (FAB M1, M3, M4, and M5). They found Auer rods in mature neutrophils and band forms in 10 of 50 patients (20%) with AML M2 but in none of 50 patients with non-M2 AML. This finding was not related to the frequency of mature cells in the specimen or to the frequency of Auer rods in blasts. Cytogenetics did not show a consistent abnormality. The presence of Auer rods in mature granulocytes is unique to FAB M2 AML in the authors' series and supports the concept that in AML at least some of the mature myeloid cells are involved in the leukemic process.