**Core Concept**
Neuroblastoma is a type of pediatric cancer that arises from the neural crest cells of the sympathetic nervous system. The prognosis and outcome of neuroblastoma are influenced by various genetic and molecular factors, including DNA ploidy, N-myc amplification, and expression of specific receptors.

**Why the Correct Answer is Right**
Trk A (also known as NTRK1) is a high-affinity receptor for nerve growth factor (NGF). In neuroblastoma, Trk A expression is associated with a favorable outcome, as it indicates a more differentiated and less aggressive tumor. This is because Trk A expression is linked to a better response to chemotherapy and a lower risk of relapse. In contrast, N-myc amplification is a marker of aggressive disease and poor prognosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Diploidy refers to the presence of 46 chromosomes, which is a normal diploid number in humans. However, in neuroblastoma, diploidy is not a favorable prognostic factor, as it is often associated with a more aggressive disease.

**Option B:** N-myc amplification is a genetic event that leads to overexpression of the N-myc protein, which drives tumor growth and proliferation. This is a marker of poor prognosis in neuroblastoma, associated with aggressive disease and a higher risk of relapse.

**Option C:** Chromosome 1p deletion is a common genetic abnormality in neuroblastoma, but it is not associated with a favorable outcome. In fact, 1p deletions are often linked to a more aggressive disease and a poorer prognosis.

**Clinical Pearl / High-Yield Fact**
In neuroblastoma, the presence of Trk A expression is a key predictor of a favorable outcome. This is because Trk A expression is associated with a more differentiated tumor and a better response to chemotherapy.

**Correct Answer Line**
✓ Correct Answer: D. Trk A expression