A Phase II Study of Decitabine Followed By Allogeneic Hematopoietic Stem Cell Transplantation in High-Risk Patients with Myeloid Malignancies

Abstract Introduction: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only curative therapy for myelodysplastic syndrome (MDS) and high-risk acute myeloid leukemia (AML). Patients with high-risk disease have a markedly increased risk of relapse and death following transplant (Armand et al, Blood, 2014). Those who remain disease-free are at risk of severe morbidity from graft-versus- host-disease (GvHD). These issues highlight the importance of improved allo-HSCT platforms designed to reduce relapse rate without increasing risk of GvHD. Decitabine has minimal non-hematologic toxicity and proven efficacy in myeloid diseases (Blum et al, PNAS, 2010). Use of post-transplant cyclophosphamide has demonstrated improved rates of GvHD following allo-HSCT using haplo-identical donors (Bashey et al, JCO, 2013). No studies have reported on outcomes in patients undergoing decitabine immediately prior to transplantation followed by post-transplant cyclophosphamide (PTCy). We hypothesized that the combination of decitabine induction prior to transplant and PTCy would be safe and result in improved disease control with low rates of GVHD, translating into improved survival in a high-risk transplant cohort. Methods In this single-arm, single institution trial, eligible patients received 10 days of IV decitabine at 20mg/m2 no sooner than 24 days and no later than 17 days prior to conditioning. Myeloablative conditioning included fludarabine (50mg/m2 day-5-2), busulfan (IV 3.2mg/kg/day -5-2), and 4 Gy total body irradiation on day -1. Patients above age 65 received a 25% busulfan dose reduction. Patients received a fully or partially matched related bone marrow graft on day 0. GvHD prophylaxis included 50mg/kg of IV cyclophosphamide on day +3-4. Patients with fully matched donors received only PTCy while those with partially matched donors also received mycophenolate mofetil through day +35 and tacrolimus through day +180. Results We enrolled 20 patients, fifteen patients with AML and 5 with MDS. The cohort had a median age of 64 (29-73) and was predominantly male (14/20, 70%). Eight (40%) patients scored as high risk by the HSCT comorbidity index. Eighteen patients (90%) had a high or very high-risk score by the refined disease risk index. All patients received decitabine and 18/20 (90%) underwent transplantation; 2 patients did not receive a transplant due to infectious complications. The majority of patients received a haplo-identical graft (13/18, 72%), and the remaining 5 received a matched related graft. Outcomes are reported in table 2 and figure 1. There were no engraftment failures. Five patients, 3 MDS and 2 AML, are long-term survivors with median follow-up over 3 years. One patient developed donor derived MDS and required a second transplant. Most transplanted patients (13/18, 72%) survived to day 100 with a median post-transplant survival of 138 days. There were 15 deaths on study with the majority due to underlying disease. Six patients (6/20, 30%) died of infectious complications or did not receive a transplant due to infection. Incidence of grade 3-4 acute GvHD was low among those surviving at least 40 days from transplant (3/17, 17%). There were also low rates of chronic GvHD among the 12 patients alive without ongoing GvHD at day 100 (2/12, 17%). Conclusions Decitabine induction followed by myeloablative conditioning in this high-risk population resulted in a high treatment related mortality of 40%. Still, outcomes fell into an expected range for high-risk myeloid disease in an elderly and comorbid population. Based on expected outcomes for high-risk patients from the literature (Armand et al, Blood, 2014), decitabine did not markedly improve overall survival outcomes, recognizing that no direct comparisons are available in our limited study population. Decitabine may increase the risk of peri-transplant infections by contributing to a cumulative immunologic insult combined with disease-related immunosuppression and transplant-related toxicity, highlighting the importance of strict vigilance for infections within this setting. Diligent monitoring may improve infectious outcomes as shown in the second half of the cohort; only two out of the latter 10 patients on protocol died of treatment related complications. There were no cases of engraftment failure. Rates of acute and chronic GvHD using a PTCy platform were low and support other studies reporting this benefit. Disclosures No relevant conflicts of interest to declare.