Outcomes of allogeneic stem cell transplantation after inotuzumab ozogamicin treatment for relapsed or refractory acute lymphoblastic leukemia

Abstract Background Attaining complete remission of acute lymphoblastic leukemia (ALL) before hematopoietic stem cell transplantation (HSCT) correlates with better post-transplant outcomes. Inotuzumab ozogamicin (InO), an anti-CD22 antibody conjugated to calicheamicin, has shown significantly higher rates of remission, minimal residual disease negativity, and HSCT versus standard chemotherapy in treating relapsed/refractory (R/R) ALL. We investigated the role of previous transplant, and proceeding directly to HSCT after remission, as factors in determining post-transplant survival in the setting of InO treatment for R/R ALL. Methods The analyzed population comprised InO-treated patients who proceeded to allogeneic HSCT in two clinical trials (phase 1/2: NCT01363297 and phase 3: NCT01564784). Overall survival (OS) was defined as time from HSCT to death (any cause). Results Of 236 InO-treated patients, 101 (43%) proceeded to allogeneic HSCT and were included in this analysis. Most received InO as first salvage (62%); 85% had no previous HSCT. Median (95% CI) post-transplant OS was 9.2 months (5.1, not estimable) with 2-year survival probability (95% CI) of 41% (32–51%). In first-HSCT patients (n=86), median (95% CI) post-transplant OS was 11.8 months (5.9, not estimable) with 2-year survival probability (95% CI) of 46% (35–56%); some patients relapsed and needed additional treatment before HSCT (n=28). Those who went directly to first HSCT upon remission with no additional salvage/induction treatment (n=73) fared best: median post-transplant OS was not reached with 2-year survival probability (95% CI) of 51% (39–62%). Conclusion In patients with R/R ALL, InO followed by allogeneic HSCT provided optimal long-term survival benefit among those with no previous HSCT who went directly to transplant after remission.