PS953 SURVIVAL OUTCOME OF SECOND ALLOGENEIC‐HCT IN ADULT ALL PATIENTS WHO RELAPSED AFTER PREVIOUS ALLOGENEIC‐HCT

Background: Allogeneic hematopoietic cell transplantation (allo‐HCT) is a potentially curative option for adult patients with acute lymphoplastic leukemia (ALL). However, no standard therapy is elucidated for patients who relapsed after allo‐HCT. Aims: We analyzed patients treated with second allo‐HCT and tried to find out risk factors for survival outcomes. Methods: We retrospectively analyzed 35 adult ALL patients (median 35 years old, range 16–66) treated with second allo‐HCT in second remission from 2010 to 2017, all of them relapsed after previous allo‐HCT (median 12.8 months, range 2.9–99.4). After second remission, most patients underwent second allo‐HCT from available donor within 6 months, but some patients with Ph‐positive ALL responding to salvage tyrosine kinase inhibitors or with isolated EMR were delayed for second allo‐HCT. Results: Of 35 patients, 3 patients were T‐ALL, 16 were Philadelphia chromosome (Ph)‐negative, and 16 were Ph‐positive B‐ALL. Extramedullary relapse (EMR) were observed in 11 patients, and 5 of them were isolated EMR without hematological relapse. At the time of second allo‐HCT, 17 were in complete remission (CR) and 18 were in CR without full hematological recovery. Among 16 Ph‐positive ALL patients, 9 were in complete molecular response, 2 were in major molecular response, and 5 were in poor molecular response. After median follow‐up of 38.2 months (range 7.5–86.3), 3‐year overall survival (OS) and disease‐free survival (DFS) were 31.9% and 26.0%, respectively. Cumulative inicidence of non‐relapse mortality (NRM) and relapse (CIR) at 3 years were 29.1% and 45.4%, respectively. Acute GVHD was observed in 17 (12 with grade I‐II, 4 with grade III, 1 with grade IV) and chronic GVHD was observed in 14 (mild 7, moderate 4, severe 3) out of 31 patients who were alive at least 100 days after HCT. We identified late relapse > 6 months and early allo‐HCT within 6 months (48.1% vs. 12.5% ; HR = 0.27, 95%CI 0.1–0.7, p  = 0.014) and chronic GVHD (49.0% vs. 27.8% ; HR = 0.28, 95%CI 0.1–0.8, p  = 0.021) showed favorable 3‐year OS in the entire cohort. Among patients with Ph‐positive subgroup, post‐HCT complete molecular response was related with superior OS (66.7% vs. 0.0% ; HR = 0.09, 95%CI 0.01–0.69, p  = 0.021). Summary/Conclusion: Our data suggested that second allo‐HCT might be a feasible choice for some patients relapsed after previous allo‐HCT as a curative treatment option when allo‐HCT is performed earlier in late relapse case. Safe salvage therapy and additional post‐HCT preemptive therapy should be considered for better transplant outcomes.