**Core Concept**
Acute Myeloid Leukemia (AML) is a heterogeneous group of malignancies characterized by the clonal expansion of myeloid blasts in the bone marrow. The prognosis of AML is influenced by various factors, including cytogenetic abnormalities, molecular mutations, and clinical features.

**Why the Correct Answer is Right**
The correct answer is associated with a poorer response to therapy and a higher risk of relapse. This factor is related to the expression of the multidrug resistance protein P-glycoprotein (P-gp) on the surface of leukemic cells, which leads to reduced intracellular accumulation of chemotherapeutic agents. The overexpression of P-gp is often linked to the presence of the multidrug resistance-associated protein 1 (MRP1) and the breast cancer resistance protein (BCRP).

**Why Each Wrong Option is Incorrect**
**Option A:** Age is an important prognostic factor in AML, but it is not the correct answer. Younger patients tend to have a better prognosis than older patients.
**Option B:** The presence of the NPM1 mutation is generally considered a favorable prognostic factor in AML.
**Option C:** The t(15;17) translocation, also known as the PML-RARA fusion, is characteristic of acute promyelocytic leukemia (APL), a subtype of AML with a relatively favorable prognosis.

**Clinical Pearl / High-Yield Fact**
The French-American-British (FAB) classification system is an outdated classification system for AML, but it is still widely used in clinical practice. The FAB system categorizes AML into eight subtypes based on the degree of maturation and the cell lineage involved.

**Correct Answer:** D.