**Core Concept**
Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia (AML) characterized by the accumulation of immature granulocytes, known as promyelocytes. The disease is often associated with specific chromosomal translocations involving the retinoic acid receptor-alpha (RAR-alpha) gene.

**Why the Correct Answer is Right**
The characteristic chromosomal translocation in APL is t(15;17), which involves the fusion of the RAR-alpha gene on chromosome 17 with the promyelocytic leukemia (PML) gene on chromosome 15. This translocation results in the formation of the PML-RAR-alpha fusion gene, which disrupts normal cell differentiation and proliferation pathways. The PML-RAR-alpha protein complex interferes with retinoic acid-mediated differentiation of promyelocytes, leading to the accumulation of these immature cells and the development of APL.

**Why Each Wrong Option is Incorrect**
* **Option A:** t(8;21) is a characteristic translocation in AML with maturation, not APL.
* **Option B:** inv(16) is associated with AML with abnormal bone marrow eosinophils, not APL.
* **Option D:** t(9;22) is the Philadelphia chromosome, characteristic of chronic myeloid leukemia (CML) and some cases of acute lymphoblastic leukemia (ALL), not APL.

**Clinical Pearl / High-Yield Fact**
The PML-RAR-alpha translocation in APL is associated with a high risk of bleeding due to disseminated intravascular coagulation (DIC). Treatment with all-trans retinoic acid (ATRA) can induce differentiation of promyelocytes and prevent DIC, but patients may still require supportive care and anticoagulation therapy.

**Correct Answer: C. t(15;17)**