**Core Concept**
Hyperdiploidy refers to the presence of more than 46 chromosomes in acute lymphoblastic leukemia (ALL), commonly seen in pediatric patients. It is associated with better response to therapy and improved survival outcomes due to more favorable genetic characteristics and increased sensitivity to chemotherapy.

**Why the Correct Answer is Right**
Hyperdiploidy is a well-established favorable prognostic factor in B-cell ALL, especially in children. Patients with hyperdiploidy typically have a higher number of chromosomes (e.g., 48–60), which correlates with better remission rates and longer overall survival. This is because hyperdiploid cells often have fewer high-risk genetic mutations and are more responsive to conventional chemotherapy regimens.

**Why Each Wrong Option is Incorrect**
Option A: High WBC count is actually a poor prognostic factor, associated with increased treatment toxicity and higher risk of relapse.
Option B: Male sex is not a significant independent prognostic factor in ALL; gender has minimal impact on outcome.
Option C: Age < 2 years is associated with a *better* prognosis in some studies, but it is not as consistently predictive as hyperdiploidy. Moreover, younger children often have hyperdiploidy, which makes this option less specific.

**Clinical Pearl / High-Yield Fact**
In pediatric ALL, hyperdiploidy is one of the strongest positive predictors of favorable outcome. It should be assessed via karyotyping and is routinely used in risk stratification protocols.

✓ Correct Answer: D. Hyperdiploidy