AML-528 Long-Term Outcomes After Haploidentical Stem Cell Transplantation (Haplo-SCT) for Hematologic Malignancies

Background: Allogeneic SCT is curative for large proportion of patients with high-risk hematologic malignancies. The introduction of posttransplant cyclophosphamide (PTCy)-based graft versus host disease (GVHD) prophylaxis led to significant improvements in haplo-SCT outcomes and a remarkable increase in its use in the past decade. We aimed from this study to assess long-term outcomes of patients who underwent haplo-SCT. Methods: We included all consecutive adult patients who had their first haplo-SCT between 2/2009 and 3/2019. Long-term survivors defined as patients who were alive and disease free at 2 years after transplant. Primary objectives: PFS and OS. Secondary objectives: cumulative incidence of relapse (CIR) and non-relapse mortality (NRM). Age, gender, KPS, DRI, HCT-CI, conditioning regimen, CMV status, and history of GVHD were included in the predictive risk-factor analysis for long-term outcomes. Results: 336 patients were identified: AML/MDS, n=196; ALL, n=55; lymphoid malignancy, n=48; MPNs, n=37. Of these, 144 patients with a median age of 45 (range, 18-72) years were disease-free at 2 years after transplant. Thirty-three percent of patients with ≥55 years, 28% had high/very-high DRI, and 30% had high HCT-CI >3. Majority received reduced intensity conditioning (88%). Prior history of acute grades 2-4 and chronic GVHD were 54 (37%) and 28 (19%) patients, respectively. The 4-year PFS and OS for all study patients were 42% and 47%, respectively. With a median follow-up of 52 months for the long-term survival group, the 4-year PFS and OS were 92% and 96%, respectively. The 4-year CIR and NRM were 4% and 3%, respectively. Age ≥ 55 was the only predictive factor in multivariate analysis for inferior PFS (HR 2.63, 95% CI: 1.01-6.84; p=0.047) and OS (HR 3.33, 95% CI: 1.08-12.23; p=0.036). Thirteen patients (9%) died in the long-term survivor group, only two of which died of relapsed disease. Secondary primary malignancy was the most frequent cause of NRM (n=4), 2 patients died from infection, 1 patient each from GVHD and sudden death, and 3 unknowns. Conclusions: Our findings suggest an excellent long-term survival for patients who were disease-free at 2 years after haplo-SCT. Late relapses were low, and age was the only predictive factor for survival.