Introduction
Allogeneic hematopoietic stem cell transplantation (AHSCT) has evolved as a curative therapy for various hematological malignancies. Regimen-related toxicity and transplant-related mortality (TRM) preclude the use of myeloablative conditioning (MAC) regimens in older and unfit patients. Reduced intensity conditioning (RIC) regimens have enabled AHSCT in such patients. There is a recent rise in use of RIC regimens even in younger patients in view of decreased toxicity and equal efficacy as reported in some studies. Fludarabine + Melphalan (FM) and Fludarabine + Treosulfan (FT) are 2 such regimens. There are no prospective randomised comparisons between these regimens. We retrospectively analysed these 2 regimens for toxicities and outcomes.
Methods
This is a retrospective single centre analysis of all consecutive patients with haematological cancers who received either FM or FT from April 2008 to December 2018. The entire cohort was divided into two groups - Matched Sibling Donor (MSD)/Matched Unrelated Donor (MUD) and Haploidentical (Haplo) transplants for analysis. We compared patient characteristics, toxicities and outcomes in both the groups based on conditioning regimen. The FT regimen consisted of fludarabine (30 mg/m2 on days − 6 to − 2) combined with treosulfan (12-14 gm/m2 on days − 6 to − 4) with or without 2 Gy TBI on day-1. The FM regimen consisted of fludarabine (30 mg/m2 on days − 7 to − 3) combined with melphalan (140 mg/m2 on day -1).Prophylaxis for GVHD consisted of calcineurin inhibitor (CNI) plus methotrexate (MTX)or mycophenolate mofetil (MMF) in MSD/MUD. Rabbit ATG (2.5-5 mg/kg) was used for MUD. Haplo transplant patients received post-transplant cyclophosphamide with CNI and MMF. Comorbidities were scored according to the HCT-CI. Disease Risk Index(DRI) and EBMT score were recorded for all patients. Neutrophil (NE) and platelet engraftment (PE) were defined as per standard criteria. Early toxicity after AHCT was graded according to CTCAE version 4. Total parenteral nutrition (TPN) was used in patients as per the physician's discretion. Acute GVHD and chronic GVHD were recorded according to standard criteria. All patients underwent chimerism studies at day 15, 30 and then monthly for 1 year. Mixed chimerism was defined as > 5% to < 95% donor chimerism. The toxicities in various arms were compared by Chi-square test or Fisher exact test, while OS was calculated by Kaplan Meier method and the survival probabilities were compared using log-rank test. Competing risk analysis was used to calculate cumulative incidence of relapse and TRM.
Results
The study included 138 patients, 98 males and 40 females. The diagnoses were AML- 53, ALL- 30, MDS/MPN- 49 and lymphoma -6. Patient characteristics are outlined in Table 1. MSD/MUD transplants were 105 (FM- 94; FT-11); 33 were Haplo (FM-17; FT-16) transplants. PBSC was the stem cell graft in 136 (99%) patients.
In both MSD/MUD and Haplo groups, there were no significant differences in median age, gender, pre transplant CMV status, HCT-CI and EBMT score between the two conditioning regimens. In MSD/MUD group, significantly more patients had high/very high DRI in FT arm (45% vs 17%; P=0.056)
Comparison of engraftment and toxicity variables of both FM and FT arms are outlined in Table 2. In MSD/MUD group, 44 (47%) patients in FM arm had grade 3/4 oral mucositis compared to 1 (9%) in FT arm (P=0.02). Corresponding numbers were 7 (41%) and 1 (6%) in Haplo group (P=0.039). Grade 3/4 diarrhoea was higher in the FM vs FT arm of Haplo group (41% vs 6%; P=0.039) but not in the MSD/MUD cohort. More patients received TPN in the FM arms of both MSD/MUD and Haplo groups (Table 2). Incidence of grade III-IV acute GVHD was higher in FT vs FM in MSD/MUD group (27% vs 17%; P=0.04).
The median follow up of entire cohort was 4.8 years. The OS (figure 1) at 5 years was 62% in FM arm of MSD/MUD group vs 53% in FT arm (P=NS). Similarly OS (figure 2) at 5 years was 41% and 28 %( P=NS) in FM and FT arms respectively of Haplo group. The cumulative incidence of TRM and relapse at 2 years were not different in FM and FT arms of both MSD/MUD and Haplo groups (Table 2).
Conclusion
Grade 3 and 4 oral mucositis and diarrhoea were significantly less with FT than FM in both MSD/MUD and Haplo groups. FT provided comparable outcomes to FM in the MSD / MUD group in spite of having higher proportions of patients with high / very high DRI. Prospective randomised studies are required to compare various RIC regimens.
No relevant conflicts of interest to declare.
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