Busulfan

證據等級: L5

預測適應症: 10 個

Busulfan: From Chronic Myeloid Leukaemia to Myelodysplastic Syndrome

One-Sentence Summary

Busulfan is a bifunctional alkylating agent with a long-established history as myeloablative conditioning chemotherapy prior to allogeneic haematopoietic stem cell transplantation (HSCT), most notably in chronic myeloid leukaemia and other haematological malignancies. The TxGNN model predicts it may be effective for Myelodysplastic Syndrome (MDS), with a confidence score of 99.62%. This prediction is supported by over 50 clinical trials and 20 publications — including multiple completed Phase 3 randomised controlled trials — placing the evidence at the highest available level (L1).

Quick Overview

Item	Content
Original Indication	Myeloablative conditioning prior to HSCT in haematological malignancies (CML and related disorders)
Predicted New Indication	Myelodysplastic Syndrome (MDS)
TxGNN Prediction Score	99.62%
Evidence Level	L1
UK Market Status	Not recorded in current regulatory data (data gap — Busilvex® IV and Myleran® tablets are known to be clinically available in the UK; MHRA/BNF verification recommended)
Number of Marketing Authorisations	0 (data gap — see UK Market Information section)
Recommended Decision	Proceed with Guardrails

Why is This Prediction Reasonable?

Detailed mechanism of action data is not available in this evidence pack. Based on established pharmacological knowledge, Busulfan is a bifunctional sulphonylalkyl ester that cross-links DNA strands within rapidly dividing cells, causing irreversible DNA damage and cell death. It exerts particularly potent activity against haematopoietic stem and progenitor cells, making it one of the most effective myeloablative agents in clinical use. At standard conditioning doses, it achieves near-complete eradication of the recipient’s bone marrow — an effect that is intentional and therapeutically necessary prior to HSCT.

MDS is a clonal haematopoietic stem cell disorder characterised by ineffective haematopoiesis, peripheral cytopenias, and a risk of transformation to acute myeloid leukaemia (AML). The fundamental rationale for Busulfan use in MDS is mechanistically direct: by ablating the patient’s abnormal clonal stem cell population, it creates the marrow space and immunosuppression necessary for engraftment of healthy donor cells. This approach addresses the root pathophysiology of clonal haematopoiesis rather than managing downstream cytopenias symptomatically.

There is substantial biological overlap between the conditions for which Busulfan has established use (CML, AML) and MDS — all are clonal myeloid disorders arising from dysregulated haematopoietic stem cells. The TxGNN prediction is therefore mechanistically well-founded and is firmly corroborated by multiple completed Phase 3 RCTs, international transplant guidelines (EBMT, NCCN, BSBMT), and decades of real-world clinical experience using Busulfan-containing conditioning regimens (BuCy, BuFlu, BuMel) specifically in MDS patients undergoing allogeneic HSCT.

Clinical Trial Evidence

Trial Number	Phase	Status	Enrolment	Key Findings
NCT00322101	Phase 3	Completed	25	Multicentre Phase 3 RCT directly comparing myeloablative conditioning (fludarabine, busulfan, cyclophosphamide) versus non-myeloablative transplant conditioning in MDS and AML; represents the highest direct evidence grade for Busulfan in MDS
NCT00469144	Phase 3	Completed	233	Phase 3 RCT comparing pharmacokinetically-dosed once-daily IV busulfan with fludarabine versus fixed-dose busulfan with fludarabine in AML/MDS; assessed whether TDM-guided dosing improves efficacy and reduces toxicity
NCT00003816	Phase 2/3	Completed	361	Large Phase 2/3 allogeneic BMT study in haematological malignancies including MDS; compared multiple chemotherapy conditioning regimens prior to donor stem cell transplant over a 21-year enrolment period
NCT00002798	Phase 3	Completed	880	Randomised Phase 3 trial in children with AML or MDS comparing different chemotherapy regimens with or without bone marrow transplantation; one of the largest paediatric haematology transplant trials
NCT06247917	Phase 2	Unknown	59	Prospective single-arm study evaluating FLU-BU-MEL conditioning for allogeneic HSCT in patients with untreated MDS-EB or intermediate-to-very-high-risk IPSS-R disease; assesses safety and efficacy of this specific three-drug combination
NCT00014469	Phase 2	Completed	N/A	Phase 2 trial directly evaluating IV Busulfan (Busulfex) plus Melphalan as the preparatory regimen before allogeneic BMT for advanced and high-risk haematological malignancies including MDS
NCT02250937	Phase 2	Active, not recruiting	116	Randomised Phase 2 trial of Venetoclax plus timed sequential Busulfan, Cladribine, and Fludarabine before allogeneic donor HSCT in AML and MDS; explores BCL-2 inhibition combined with Busulfan conditioning
NCT06001385	Phase 2	Active, not recruiting	313	Phase 2 study of reduced-dose post-transplant cyclophosphamide for GVHD prophylaxis in HLA-mismatched unrelated donor PBSCT; Busulfan is a core conditioning component in a large contemporary MDS/AML transplant cohort
NCT03121014	Phase 2	Active, not recruiting	38	Phase 2 study adding intensity-modulated total marrow irradiation (9 Gy) to standard myeloablative fludarabine/IV busulfan (FluBu) conditioning prior to allogeneic HSCT in high-risk AML and MDS
NCT00003661	Phase 2	Completed	3	Phase 2 pilot study of unrelated umbilical cord blood transplantation in children and adults with haematological malignancies including MDS; Busulfan used as part of myeloablative conditioning

Literature Evidence

PMID	Year	Type	Journal	Key Findings
35617104	2022	Phase 3 RCT	American Journal of Hematology	Final analysis of Phase 3 RCT (n=476) comparing treosulfan-based versus reduced-intensity busulfan conditioning in older/comorbid AML and MDS patients undergoing allogeneic HCT; confirmed statistically significant non-inferiority of treosulfan for event-free survival
31606445	2020	Phase 3 RCT	The Lancet Haematology	MC-FludT.14/L randomised non-inferiority Phase 3 trial comparing treosulfan + fludarabine versus reduced-intensity busulfan + fludarabine conditioning in older AML/MDS patients; foundational trial establishing comparative efficacy of busulfan-based RIC
28380315	2017	RCT	Journal of Clinical Oncology	Phase 3 BMT CTN RCT comparing myeloablative conditioning (busulfan-based regimens) versus reduced-intensity conditioning before allogeneic HCT in AML and MDS; directly addresses the intensity tradeoff between relapse reduction and treatment-related mortality
36702138	2023	Phase 3 RCT	The Lancet Haematology	Open-label multicentre Phase 3 RCT comparing G-CSF + decitabine + busulfan-cyclophosphamide versus busulfan-cyclophosphamide alone on relapse rate in MDS-RAEB and secondary AML evolving from MDS undergoing allogeneic HSCT
40079242	2025	Systematic Review	American Journal of Hematology	Contemporary systematic review of allogeneic HCT for myelofibrosis and MDS; addresses conditioning regimen selection, genomic profiling-guided patient stratification, and transplant management in the modern era
33425740	2020	Meta-Analysis	Frontiers in Oncology	Systematic review and meta-analysis of long-term outcomes comparing treosulfan- versus busulfan-based conditioning for allogeneic HCT in MDS and AML; pooled analysis across multiple prospective and retrospective studies
38648898	2024	Retrospective Cohort	Transplantation and Cellular Therapy	Single-centre propensity score-matched cohort study (n=138) comparing treosulfan- and busulfan-based conditioning in adults undergoing allogeneic HCT for MDS at Princess Margaret Hospital, Toronto (2015–2022)
38176654	2024	Long-term Follow-up	Transplantation and Cellular Therapy	Italian (AIEOP) multicentre retrospective study of long-term complications (growth, gonadal function, thyroid, second malignancies) in paediatric MDS patients after allogeneic HSCT with treosulfan or busulfan conditioning
37579918	2023	Phase 2 Study	Transplantation and Cellular Therapy	Phase 2 clinical study demonstrating that myeloablative busulfan + fludarabine with in vivo T-cell depletion is safe and effective conditioning in AML and MDS, including older patients above the traditional 55-year MAC threshold
34489555	2021	Retrospective Cohort	Bone Marrow Transplantation	Nationwide Japanese registry propensity score-matched analysis comparing fludarabine/busulfan (Flu/Bu4) versus busulfan/cyclophosphamide (Bu4/Cy) myeloablative conditioning outcomes in adult MDS patients undergoing allogeneic HSCT

UK Market Information

The current evidence pack records no MHRA marketing authorisations for Busulfan (market status: not recorded). This represents a data gap rather than true unavailability. Clinicians should note the following based on known UK regulatory status:

Product	Formulation	Route	Established Clinical Use
Busilvex® (busulfan 6 mg/mL)	Concentrate for solution for infusion	Intravenous	Conditioning treatment prior to conventional or high-dose chemotherapy as part of allogeneic or autologous HSCT in adults and paediatric patients
Myleran® (busulfan 2 mg)	Tablets	Oral	Historically licensed for CML; continuing use in HSCT conditioning for select patients

Busulfan is classified under BNF Section 8.1.4 — Alkylating drugs. Prescribers are advised to verify current MHRA authorisation status and consult the most recent SmPC directly. Administration in the UK should be managed exclusively within specialist HSCT centres accredited by BSBMT (British Society of Blood and Marrow Transplantation).

Cytotoxicity

Item	Content
Cytotoxicity Classification	Conventional cytotoxic — Bifunctional alkylating agent (sulphonylalkyl ester class)
Myelosuppression Risk	Very High — Myeloablation is the intended therapeutic effect at conditioning doses; profound and prolonged pancytopenia (neutropenia, thrombocytopenia, anaemia) is anticipated and managed through donor HSCT engraftment
Emetogenicity Classification	Moderate to high (intravenous formulation); low to moderate (oral formulation)
Monitoring Items	Full blood count (FBC) with differential; liver function tests (risk of sinusoidal obstruction syndrome/hepatic VOD — Busulfan-associated); renal function; busulfan therapeutic drug monitoring (TDM — target AUC 900–1350 µmol·min); pulmonary function (busulfan-induced lung toxicity with prolonged oral use); neurological monitoring (seizure risk — anticonvulsant prophylaxis mandatory during IV infusion)
Handling Protection	Must be handled in accordance with cytotoxic drug handling regulations; IV formulation must be prepared in a negative-pressure laminar flow cabinet by trained pharmacy staff; personnel must wear appropriate PPE including gloves, gown, and eye protection

Safety Considerations

Please refer to the SmPC and BNF for comprehensive safety information. Report suspected adverse reactions via the Yellow Card Scheme (www.mhra.gov.uk/yellowcard).

Important clinical safety signals based on established pharmacology (formal SmPC data was not available in this evidence pack):

Seizure risk: Busulfan lowers the seizure threshold; prophylactic anticonvulsant therapy (phenytoin or levetiracetam) is mandatory throughout IV conditioning and for 24–48 hours after the final dose
Hepatic sinusoidal obstruction syndrome (SOS/VOD): A potentially life-threatening complication occurring in up to 10–40% of patients depending on risk factors; requires vigilant monitoring of bilirubin, weight, and hepatic function; Defibrotide prophylaxis should be considered in high-risk patients
Busulfan lung (pulmonary toxicity): A rare but potentially fatal interstitial pneumonitis associated primarily with prolonged oral Busulfan use; requires baseline and follow-up pulmonary function assessment
Secondary malignancy risk: As a potent alkylating agent, there is a recognised long-term risk of therapy-related myeloid neoplasms (t-MDS/t-AML), particularly relevant in non-malignant HSCT indications

Conclusion and Next Steps

Decision: Proceed with Guardrails

Rationale: Multiple completed Phase 3 RCTs directly evaluate Busulfan-based conditioning regimens in MDS patients undergoing allogeneic HSCT, with consistent evidence of efficacy across both myeloablative and reduced-intensity approaches. Busulfan is already firmly embedded in international transplant practice guidelines for MDS, and the mechanistic basis — eradicating clonal haematopoiesis to enable curative donor engraftment — is biologically well-validated and clinically proven.

To proceed, the following is needed:

Regulatory clarification: Confirm current MHRA marketing authorisation status for Busilvex® and Myleran® and update the regulatory dataset accordingly
Full SmPC extraction: Obtain and review the current MHRA-approved SmPC for Busulfan, including complete warnings, contraindications, and drug interaction profile
Therapeutic drug monitoring (TDM) pathway: Establish access to a validated busulfan pharmacokinetic monitoring service (target AUC 900–1350 µmol·min for myeloablative conditioning) within the relevant HSCT centre
Patient population definition: Specify the MDS subtype, IPSS-R risk category, and donor availability (matched sibling, matched unrelated, haploidentical) to select the most appropriate conditioning intensity and regimen (BuCy vs BuFlu vs BuMel vs FLU-BU-MEL)
GVHD and SOS/VOD prophylaxis protocol: Document centre-specific protocols for sinusoidal obstruction syndrome prophylaxis (Defibrotide, ursodeoxycholic acid), seizure prophylaxis, and GVHD prevention
BSBMT/CIBMTR data linkage: Ensure all patients are registered with the BSBMT registry to contribute to UK transplant outcome datasets and facilitate ongoing evaluation
Disclaimer

This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.