Auer rod

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 M2 and M3 acute myeloid leukemia and in myelodysplastic syndrome. They are composed of fused lysosomes and contain peroxidase, lysosomal enzymes, and large crystalline inclusions.

They are also used to distinguish the pre-leukemia myelodysplastic syndromes: refractory anemia with excess blasts 2 (which has Auer rods) from RAEB 1 (which does not).

Eponym
These cytoplasmic inclusions are named for John Auer, an American physiologist (1875-1948).