**Core Concept**
Auer rods are abnormal cytoplasmic inclusions found in the blast cells of patients with acute myeloid leukemia (AML), particularly in the M3 subtype (acute promyelocytic leukemia). These structures are composed of azurophilic granules that have aggregated to form needle-like or rod-like structures.

**Why the Correct Answer is Right**
Auer rods are a hallmark feature of AML, especially in the M3 subtype. They are thought to be formed due to the abnormal maturation of myeloid cells, leading to the accumulation of azurophilic granules in the cytoplasm. The presence of Auer rods in bone marrow or peripheral blood smears is a diagnostic criterion for AML. The M3 subtype of AML is characterized by the presence of Auer rods, as well as other morphological features such as hypergranulation and hyperbasophilic cytoplasm.

**Why Each Wrong Option is Incorrect**
* **Option A:** Auer rods are not typically seen in chronic myeloid leukemia (CML), which is a type of myeloproliferative neoplasm characterized by the presence of the Philadelphia chromosome.
* **Option B:** While Auer rods can be seen in some cases of acute lymphoblastic leukemia (ALL), they are not a characteristic feature of this disease.
* **Option C:** Auer rods are not typically seen in myelodysplastic syndromes (MDS), which are a group of clonal hematopoietic disorders characterized by ineffective hematopoiesis and the presence of dysplastic cells.

**Clinical Pearl / High-Yield Fact**
Auer rods are a key diagnostic feature of AML, and their presence should prompt further investigation to rule out other causes of abnormal cytology. In particular, Auer rods are a characteristic feature of the M3 subtype of AML, which is associated with a high risk of disseminated intravascular coagulation (DIC) and other complications.

**Correct Answer:** D.