A 3-year-old child presents with easy bruising, pallor, and hepatosplenomegaly. Complete blood count shows: Hb 7 g/dL, WBC 85,000/mm³ (predominantly blasts), platelets 40,000/mm³. Bone marrow biopsy confirms acute lymphoblastic leukemia. Flow cytometry shows CD10+, CD19+, CD34+, TdT+. Which chromosomal abnormality in pediatric ALL confers the BEST prognosis?
- A t(9;22) — Philadelphia chromosome (BCR-ABL1)
- B t(4;11) — KMT2A-AFF1 rearrangement
- C t(12;21) — ETV6-RUNX1 (TEL-AML1) translocation ✓
- D Hypodiploidy (fewer than 44 chromosomes)
Correct answer: C. t(12;21) — ETV6-RUNX1 (TEL-AML1) translocation
Explanation
The t(12;21)(p13;q22) translocation creating the ETV6-RUNX1 (formerly TEL-AML1) fusion gene is the most common structural chromosomal abnormality in pediatric B-cell ALL (~25% of cases) and carries the most favorable prognosis, with event-free survival rates exceeding 90%. High hyperdiploidy (>50 chromosomes) is also favorable. In contrast, t(9;22)/BCR-ABL1 (Philadelphia chromosome, ~3-5% pediatric ALL) confers poor prognosis requiring TKI therapy; t(4;11)/KMT2A-AFF1 is seen in infant ALL with very poor prognosis; hypodiploidy (< 44 chromosomes) is the worst cytogenetic group in ALL.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.