Auer rod

Auer rods (or Auer bodies) are large, crystalline cytoplasmic inclusion bodies sometimes observed in myeloid blast cells during acute myeloid leukemia, acute promyelocytic leukemia, high-grade myelodysplastic syndromes and myeloproliferative disorders. Composed of fused lysosomes and rich in lysosomal enzymes, Auer rods are azurophilic and can resemble needles, commas, diamonds, rectangles, corkscrews, or (rarely) granules.