A 34-year-old man presents to the emergency department with symptoms of fatigue, weakness, nose bleeds, and palpitations with exertion. The symptoms started 1 week ago and are getting worse every day. He has no prior health issues and is not taking any medications. On examination, he is pale, blood pressure 110/70 mm Hg, pulse 100/min, heart sounds are normal, lungs are clear, and he has multiple petechiae and bruises on his legs.His blood count is abnormal; hemoglobin 8.5 g/dL, white blood cells (WBCs) 4000/mL, platelets 50,000/mL, and there are blast cells in the peripheral blood. He is diagnosed with acute promyelocytic leukemia (AML-M3). (See Figure below) Which of the following is a characteristic of this acute myelogenous leukemia?

**Core Concept**
Acute promyelocytic leukemia (AML-M3) is a subtype of acute myelogenous leukemia (AML) characterized by the accumulation of abnormal promyelocytes in the bone marrow, leading to a severe deficiency in normal blood cells.

**Why the Correct Answer is Right**
The characteristic feature of AML-M3 is the presence of a specific chromosomal translocation, t(15;17), which results in the fusion of the retinoic acid receptor-alpha (RAR-alpha) gene with the promyelocytic leukemia (PML) gene. This fusion gene, PML-RAR-alpha, disrupts normal cell maturation, leading to the accumulation of promyelocytes. The PML-RAR-alpha fusion protein inhibits the transcription of genes involved in granulocytic differentiation, causing a block in cell maturation.

**Why Each Wrong Option is Incorrect**
**Option A:** AML-M3 is not characterized by the presence of a Philadelphia chromosome, which is a hallmark of chronic myeloid leukemia (CML).

**Option B:** AML-M3 does not typically present with a high number of blasts in the peripheral blood, as seen in other subtypes of AML. The presence of blast cells in the peripheral blood is a diagnostic criterion for AML, but the number and distribution of blasts can vary depending on the subtype.

**Option C:** AML-M3 does not typically present with a high white blood cell count. In fact, the patient may present with a normal or decreased WBC count due to the block in cell maturation.

**Option D:** AML-M3 does not typically present with a high platelet count. In fact, the patient may present with thrombocytopenia due to the consumption of platelets in the microcirculation.

**Clinical Pearl / High-Yield Fact**
AML-M3 is associated with a high risk of bleeding complications due to the consumption of platelets and coagulation factor deficiencies. Patients with AML-M3 may require aggressive thromboprophylaxis and supportive care to manage bleeding complications.

**Correct Answer:** C. The presence of a specific chromosomal translocation, t(15;17), is a characteristic feature of AML-M3.

✓ Correct Answer: D. Auer bodies in blast cells