PB2325 OUTCOMES OF ALLOGENEIC HEMATOPOIETIC STEM CELL TRANSPLANTATION (ALLOHCT) FOR MYELOFIBROSIS (MF) – A SINGLE CENTER EXPERIENCE

Background: Allogeneic transplantation (alloHCT) is the only curative treatment modality for MF. Older age at diagnosis and age‐related comorbidities make most patients ineligible for alloHCT, given concerns for non‐relapse mortality (NRM). Utilization of alloHCT for MF is increasing recently with reduced intensity conditioning (RIC) approach. Herein, we report the outcomes of alloHCT for MF at Medical College of Wisconsin (MCW), Milwaukee, WI. Aims: Evaluate and report the outcomes of alloHCT for MF at Medical College of Wisconsin (MCW), Milwaukee, WI. Methods: We retrospectively reviewed the outcomes of 37 recipients of alloHCT for MF performed between 2009 and 2018. All patients with JAK2 mutation (68%) and/or constitutional symptoms received ruxolitinib for at least 4 months prior to HCT, and those with splenomegaly >22 cm received pre‐transplant splenic radiation. Survival outcomes (overall [OS] and relapse‐free survival [RFS]) were analyzed using Kaplan‐Meier method and compared between groups using log‐rank test. Results: Median age was 60 years (range, 40‐74): 68% carried JAK2 driver mutation. 46% evolved from primary ET or PV and 11% had/developed MDS, in addition, pre‐HCT. Three‐quarters of the cohort had WHO grade 3 MF before HCT. 84% received ruxolitinib and 11% were treated with hypomethylating chemotherapy prior to transplant; 90% had splenomegaly, 35% received splenic radiation. Six patients had cirrhosis and portal hypertension (PHTN), and another 4 had PHTN without cirrhosis. Twenty‐two patients (60%) received reduced intensity conditioning and all patients received peripheral blood transplant. Sixteen (43%) patients had matched sibling donor, and others had unrelated (n = 20) or haploidentical related donor (n = 1). HCT‐CI score was ≥3 in 61%; 60% had KPS ≥90. The median follow‐up of survivors was 30 months (range, 7.1‐109). The 3‐year OS and RFS were 87% and 84%, respectively. Only one patient relapsed (with acute myeloid leukemia) 15 months post‐HCT. NRM at 2 years was 11%; causes of death were sepsis (n = 3) and GVHD (n = 1). Karyotype was the only predictor significantly associated with OS on univariate analysis (favorable/standard‐risk vs. unfavorable, HR 5.3, p = 0.02). Summary/Conclusion: Despite advanced age (51% over 60 years; 24% over 65 years) and 61% with HCT‐CI ≥ 3, we report high‐quality single‐center survival data in a carefully‐selected MF patient population. We speculate that the use of ruxolitinib and splenic radiation pre‐HCT, busulfan‐based RIC regimen and higher CD34+ cell dose (median, 7.8 × 10 6 /kg) contributed to the improved outcomes in this series.