What is the latest study on conditioning regimens for pediatric acute myeloid leukemia (AML) allogeneic stem cell transplantation?

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Last updated: October 25, 2026 • View editorial policy

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Latest Evidence on Conditioning Regimens for Pediatric AML Transplant

The most recent high-quality studies from 2026 demonstrate that TBI/busulfan/fludarabine conditioning achieves superior outcomes (73% 5-year event-free survival) for pediatric AML patients in second complete remission, while treosulfan-based and cladribine-based regimens show promise as alternatives with reduced toxicity profiles.

Current Guideline Framework

The 2012 international expert panel consensus establishes that myeloablative chemotherapy-based conditioning is preferred over total body irradiation (TBI) alone due to fewer late effects and lower risk of secondary malignancies 1. However, the guidelines acknowledge that the optimal conditioning regimen remains unidentified and unstandardized 1.

Most Recent Evidence (2026 Studies)

For Second Complete Remission (CR2)

The strongest recent evidence comes from a 2026 study comparing conditioning regimens in pediatric AML patients undergoing HSCT in CR2 2. Patients receiving TBI (8 Gray) combined with busulfan and fludarabine (TBI/Bu/Flu) achieved significantly superior 5-year event-free survival of 73.0% compared to only 23.1% with busulfan/fludarabine alone (p=0.004) 2. This represents a dramatic improvement over historical outcomes, with:

  • 5-year cumulative relapse incidence: 30.7%
  • Non-relapse mortality: 11.8%
  • Overall survival: 66.8%

Notably, this regimen performed equally well regardless of donor type, including haploidentical family donors (74.4% of patients) 2.

Alternative Regimens with Reduced Toxicity

Treosulfan-Based Conditioning

A 2026 Polish study of 85 children with AML in CR1 or CR2 demonstrates that treosulfan-based regimens provide an effective alternative with markedly reduced toxicity 3:

  • Zero early regimen-related mortality
  • Oral mucositis (grade ≥3): only 15.3%
  • Non-relapse mortality: 5.9%
  • 5-year relapse-free survival: 76.9%
  • 5-year overall survival: 75.4%

This regimen is particularly valuable for patients with pre-transplant risk factors for severe toxicity 3.

Cladribine-Based Conditioning

A 2026 study of cladribine-containing regimens in relapsed/refractory pediatric AML showed 4:

  • 1-year overall survival: 87.5%
  • 1-year disease-free survival: 87.4%
  • Relapse rate: only 6.3%
  • Mild regimen-related toxicity (grade I/II: 31.3%; no grade III/IV)
  • Effective even in MRD-positive patients (18.75% of cohort)

Clinical Decision Algorithm

For CR2 Patients:

  1. First-line choice: TBI/busulfan/fludarabine conditioning 2
    • Provides best event-free survival (73%)
    • Acceptable toxicity profile
    • Effective across all donor types

For CR1 High-Risk or Patients with Toxicity Concerns:

  1. Consider treosulfan-based regimens 3

    • Especially if pre-existing organ dysfunction
    • Comparable survival to traditional regimens
    • Significantly reduced early toxicity

  2. Consider cladribine-based regimens for relapsed/refractory disease 4

    • Particularly if MRD-positive pre-transplant
    • Lower gastrointestinal and renal toxicity

Important Caveats

Risk Stratification Remains Critical

  • Favorable-risk patients should NOT receive HSCT in first CR 1
  • Intermediate and high-risk patients: benefit must be balanced against toxicity 1
  • All relapsed AML patients in CR2 should be offered allo-HSCT 1

Donor Selection

Recent improvements in unrelated donor outcomes have changed the landscape 1. The 2026 TBI/Bu/Flu study showed no difference in outcomes between haploidentical and other donor types 2, suggesting donor availability should not be a barrier.

MRD Status

High MRD levels before HSCT predict poorer outcomes 1. The cladribine study suggests this regimen may partially overcome MRD positivity 4, though numbers are small.

Key Pitfalls to Avoid

  1. Do not use TBI alone - always combine with chemotherapy to reduce late effects 1
  2. Do not use autologous HSCT in first CR - no survival benefit demonstrated 1
  3. Do not delay transplant in CR2 - all patients should proceed to allo-HSCT 1
  4. Do not use standard busulfan/fludarabine in CR2 - inferior to TBI-containing regimens 2

The field has evolved significantly, with 2026 data showing that TBI can be safely reintroduced when combined with reduced-dose (8 Gray) and modern chemotherapy, contradicting older recommendations to avoid TBI entirely. Alternative regimens (treosulfan, cladribine) provide excellent options for toxicity reduction without compromising efficacy.

References

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