Total Marrow and Lymphoid Irradiation in Combination with Cyclophosphamide and Etoposide Before Haematopoietic Cell Transplantation for Relapsed or Refractory Acute Leukaemia: a Single-Centre, Open-Label, Phase 2 Trial

BACKGROUND:Total marrow and lymphoid irradiation delivers augmented doses of radiation to the bone marrow and lymph nodes while maintaining low doses to vital organs. We aimed to assess the effectiveness of combining total marrow and lymphoid irradiation (2000 cGy to bone marrow and lymph nodes) with high-dose cyclophosphamide and etoposide as a conditioning regimen before allogeneic haematopoietic cell transplantation (HCT) in patients with relapsed or refractory acute leukaemia. METHODS:This single-centre, open-label, phase 2 trial with an initial six-patient safety lead-in, conducted in the USA, enrolled patients aged between 16 and 60 years with relapsed or refractory acute myeloid leukaemia or acute lymphoblastic leukaemia. Total marrow and lymphoid irradiation was given on days -9 to -5, etoposide 60 mg/kg on day -4, and cyclophosphamide 100 mg/kg on day -2. Bone marrow or peripheral blood stem cells from sibling or matched or one allele mismatched unrelated donors were infused on day 0. Graft versus host disease prophylaxis consisted of tacrolimus and sirolimus. The primary endpoint for the initial safety lead-in segment was toxicity and for the phase 2 study was 2-year progression-free survival. All patients who began treatment were included in the analysis. This trial is registered with ClinicalTrials.gov, NCT02094794, and is closed to accrual. FINDINGS:Between May 9, 2014, and Mar 5, 2024, 107 patients were enrolled and screened for eligibility. One did not meet eligibility criteria (uncontrolled cytomegalovirus). 106 received conditioning radiation and HCT per protocol. Median follow-up was 1·8 years (IQR 0·6-3·0) for all patients and 3·1 years (2·1-4·9) for patients who were alive at last contact. None of the six patients in the safety lead-in experienced unacceptable toxicity. 49 (46%) of 106 patients were female and 57 (54%) were male. 72 (68%) of patients were White and 22 (21%) were Asian or Pacific Islander. The 2-year estimate of progression-free survival in all patients was 34% (95% CI 25-43%). The most common grade 3-4 adverse events were cytopenias 96 (91%), metabolic disorders 83 (78%), oral mucositis 45 (42%), diarrhoea 25 (24%), nausea 21 (20%), and palmar-plantar erythrodysesthesia syndrome 11 (10%). One patient died of sinusoidal obstruction syndrome attributed to the conditioning regimen. INTERPRETATION:Adverse events were few, probably due to organ sparing by total marrow and lymphoid irradiation. Total marrow and lymphoid irradiation 2000 cGy could be safely delivered in combination with high-dose etoposide and cyclophosphamide. The regimen was associated with encouraging 2-year progression-free survival rates. FUNDING:National Institutes of Health and Accuray.