Auer rod

Auer rods can be seen in the leukemic blasts of Acute Myeloid Leukemia. Auer rods are clumps of azurophilic granular material that form elongated needles seen in the cytoplasm of leukemic blasts. They are composed of fused lysosomes and contain peroxidase, lysosomal enzymes, and large crystalline inclusions.

Diagnosis
Auer rods are classically seen in myeloid blasts of M1, M2, M3, and M4 acute leukemias.

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 were named by John Auer, an American physiologist (1875-1948).