Auer rods are clumps of azurophilic granular material that form elongated needles seen in the cytoplasm of leukemic blasts. They can be seen in the leukemic blasts of acute myeloid leukemia with maturation and acute promyelocytic leukemia and in high grade myelodysplastic syndromes and myeloproliferative syndromes. They are composed of fused lysosomes/primary neutrophilic granules and contain peroxidase, lysosomal enzymes, and large crystalline inclusions. Morphologically, the Auer "rods" come in all sizes and shapes. They have been described as needle-shapes with pointed ends, comma-shapes, and diamond-shapes; others were long and rectangular. Occasional corkscrew forms and rare granular Auer bodies were also noted. More appropriately, they can be referred to as Auer bodies.
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