A 4-year-old boy presents with pallor, petechiae, hepatosplenomegaly, and lymphadenopathy. CBC shows WBC 48,000/μL with 85% lymphoblasts, Hb 7.2 g/dL, platelets 22,000. Bone marrow confirms ALL. The cytogenetic finding that confers the BEST prognosis in childhood ALL is:

• A Philadelphia chromosome t(9;22) — BCR-ABL1 fusion
• B t(4;11) MLL rearrangement — occurs in infants, worst prognosis
• C t(1;19) E2A-PBX1 fusion — intermediate prognosis
• D High hyperdiploidy (>50 chromosomes) — best prognosis, excellent response to methotrexate and mercaptopurine ✓

Explanation

High hyperdiploidy (modal chromosome number >50, ideally 51–65) is the single cytogenetic feature associated with the best prognosis in childhood B-ALL. These cells have extra copies of chromosomes 4, 10, 17, and others, which sensitizes them to antimetabolites (methotrexate, thiopurines). Event-free survival approaches 90%. Philadelphia chromosome (BCR-ABL1) and MLL rearrangements carry poor prognosis. t(12;21) ETV6-RUNX1 (TEL-AML1) is the most common translocation in childhood ALL and carries favorable prognosis, but high hyperdiploidy is even better.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.