A Matched Controlled Analysis of Post-Transplant Cyclophosphamide (CY) Versus Tacrolimus and Mini-Dose Methotrexate in Matched Sibling and Unrelated Donor Transplant Recipients Receiving Reduced-Intensity Conditioning: Post-Transplant CY Is Associated with Higher Rates of Acute Gvhd

Abstract 4200 Graft-vs.-Host Disease (GVHD) remains a common complication following matched sibling and unrelated donor hematopoietic cell transplantation (HCT). Standard GVHD prophylaxis calls for prolonged immune suppression, typically with a calcineurin-inhibitor. Recently, post-transplant cyclophosphamide (CY) has been studied as sole prophylaxis in matched related and unrelated bone marrow (BM) transplant recipients following an ablative conditioning regimen with busulfan (Bu) and CY and demonstrated comparable rates of acute GVHD and lower rates of chronic GVHD as traditional GVHD prophylaxis regimens. We recently conducted a phase II study of post-transplant CY following a reduced-intensity conditioning (RIC) regimen of Busulfan (Bu) and Fludaribine (Flu) in matched related and unrelated donor transplants and performed a matched-control analysis comparing their results with patients who received traditional GVHD prophylaxis with tacrolimus and mini-dose methotrexate (MTX) during the same time period. Forty-nine (49) patients were enrolled onto this study. They received Flu at a dose of 40mg/m2 over 1hour followed by intravenous Bu over 3 hours targeting a daily AUC of 4,000 microMol-min on days –6 to –3. Recipients of unrelated transplants received ATG on days –3 to –1 (total dose 4 mg/kg). CY was given as sole GVHD prophylaxis at a dose of 50 mg/kg on days +3 and +4. During the same period of time, 133 patients received a RIC regimen with intravenous Bu/Flu or Flu and melphalan (Mel) and received GVHD prophylaxis with tacrolimus plus mini-dose MTX (10mg/m2 on day +1, 5mg/m2on days +3, +6, +11). Unrelated donor transplants also received ATG. A computer generated algorithm was used to identify a comparable control group from our departmental database matching, in order of priority, on age, diagnosis, disease status, donor (matched-related versus unrelated) and graft source (PB versus BM). Matched controls (control group) were successfully identified for 37 study patients (Post-Cy group). Results: The median age for the Post- CY group and control group was 61 (range, 39–72) and 62 years (range, 37–72). Eight-one (81) % of patients in both groups had AML or MDS, 3% had ALL and 16% had NHL or CLL. Fifty-nine (59) % of patients in both groups had unrelated donors and received ATG in the conditioning. Disease status for the Post-CY and control groups respectively were CR1: 14 and 14%, CR2: 8 and 11%, >CR2: 38 and 32% and Primary Induction Failure / Untreated: 40 and 32%. Seventy (70) % of the post-CY group received BM versus 48% of the control group, whereas sex mismatching (Male donor for Female patient) occurred in 22% of the post-Cy and 8% of the control group. The cumulative incidence of grade II-IV acute GVHD and chronic GVHD in the post-CY and control groups were: 46% versus 19% (Hazard Ratio (HR): 2.8, 95% CI, 1.1–6.7; p=0.02) and 14% versus 21% (HR: 0.8, 95% CI, 0.2–2.6, p=0.7). Grades III/IV acute GVHD occurred in 14% (95% CI, 6–32) of the patients in the post-CY group whereas there were no cases of grade III/IV in the control group (p=0.02). Overall, progression-free and non-relapse mortality at 2-years are shown in the table below. Conclusion: Post-transplant CY following RIC is associated with higher rates of acute GVHD, with resultant trends for higher non-relapse mortality and lower overall survival when compared to tacrolimus and mini-dose MTX. The use of post-transplant CY as a sole GVHD prophylaxis regimen should be avoided following RIC transplant in matched-related and unrelated donors. Disclosures: Off Label Use: azacitidine: off-label use as maintenance therapy following allogeneic stem cell transplant for MDS/AML.