A 7-year-old child presents with fever, pallor, and petechiae. Bone marrow examination shows 85% blasts. Flow cytometry reveals CD19+, CD10+, CD34+, TdT+. Which cytogenetic finding would best distinguish favorable-risk B-ALL from high-risk B-ALL in this patient?

Explanation

## Cytogenetic Risk Stratification in B-ALL ### Prognostic Cytogenetic Abnormalities | Cytogenetic Finding | Prognosis | Frequency in Pediatric B-ALL | |---------------------|-----------|------------------------------| | **Hyperdiploidy (>50 chr)** | **Favorable** | ~25–30% | | **t(12;21) TEL-AML1** | **Favorable** | ~20–25% | | **t(9;22) Philadelphia** | **Adverse** | ~3–5% | | **t(4;11) MLL rearrangement** | **Adverse** | ~5–10% | | **Complex karyotype (≥3 abn)** | **Adverse** | ~5–10% | | **Hypodiploidy (<45 chr)** | **Adverse** | ~5–10% | | **Normal karyotype** | **Intermediate** | ~20–30% | **Key Point:** Hyperdiploidy (>50 chromosomes) is one of the most favorable prognostic markers in pediatric B-ALL, associated with excellent long-term survival (>90%) with modern chemotherapy. This is a hallmark of common ALL (cALL) with CD19+, CD10+ immunophenotype. **High-Yield:** The patient's immunophenotype (CD19+, CD10+, CD34+, TdT+) is consistent with **common ALL (cALL)**, which frequently harbors favorable cytogenetics. Hyperdiploidy and t(12;21) TEL-AML1 are the two most common favorable findings in cALL and are strong predictors of chemotherapy responsiveness. **Clinical Pearl:** Philadelphia chromosome [t(9;22)] is the single most adverse prognostic factor in B-ALL, occurring in ~3% of pediatric cases and ~20% of adult cases. Its presence mandates intensive chemotherapy ± tyrosine kinase inhibitor (TKI) therapy. Complex karyotype also portends poor prognosis and requires intensified treatment. **Mnemonic:** **FISH for FATE: Favorable = Hyperdiploidy, t(12;21); Adverse = t(9;22), t(4;11), Complex karyotype**