Role of Remission Status and Prior Transplant in Optimizing Survival Outcomes Following Allogeneic Hematopoietic Stem Transplantation (HSCT) in Patients Who Received Inotuzumab Ozogamicin (INO) for Relapsed / Refractory (R/R) Acute Lymphoblastic Leukemia (ALL)

Introduction: Attaining complete remission (CR) prior to HSCT is associated with better outcomes post-HSCT. Inotuzumab ozogamicin (INO), an anti-CD22 antibody conjugated to calicheamicin, has shown significantly higher remission rates (CR/CRi and MRD negativity) compared with standard chemotherapy (SC) in patients (pts) with R/R ALL (Kantarjian et al. N Engl J Med. 2016). Pts treated with INO were more likely to proceed to HSCT than SC, which allowed for a higher 2-yr probability of overall survival (OS) than patients receiving SC (39% vs 29%). We investigated the role of prior transplant and proceeding directly to HSCT after attaining remission from INO administration as potential factors in determining post-HSCT survival to inform when best to use INO in R/R ALL patients.

Methods: The analysis population consisted of R/R ALL pts who were enrolled and treated with INO and proceeded to allogeneic HSCT as part of two clinical trials: Study 1010 is a Phase 1/2 trial (NCT01363297), while Study 1022 is the pivotal randomized Phase 3 (NCT01564784) trial. Full details of methods for both studies have been previously published (DeAngelo et al. Blood Adv. 2017). All reference to OS pertains to post-HSCT survival defined as time from HSCT to death from any cause.

Results: As of March 2016, out of 236 pts administered INO in the two studies (Study 1010, n=72; Study 1022, n=164), 101 (43%) proceeded to allogeneic HSCT and were included in this analysis. Median age was 37 y (range 20-71) with 55% males. The majority of pts received INO as first salvage treatment (62%) and 85% had no prior SCT. Most pts received matched HSCTs (related = 25%; unrelated = 45%) with peripheral blood as the predominant cell source (62%). The conditioning regimens were mainly myeloablative regimens (60%) and predominantly TBI-based (62%). Dual alkylators were used in 13% of pts, while thiotepa was used in 8%. The Figure shows post-transplant survival in the different INO populations: The median OS post-HSCT for all pts (n=101) who received INO and proceeded to HSCT was 9.2 mos with a 2-yr survival probability of 41% (95% confidence interval [CI] 31-51%). In patients with first HSCT (n=86) the median OS post-HSCT was 11.8 mos with a 2-yr survival probability of 46% (95% CI 35-56%). Of note, some patients lost CR while waiting for HSCT and had to receive additional treatments before proceeding to HSCT (n=28). Those pts who went directly to first HSCT after attaining remission with no intervening additional treatment (n=73) fared best, with median OS post-HSCT not reached with a 2-yr survival probability of 51% (95% CI 39-62%). In the latter group, 59/73 (80%) attained MRD negativity, and 49/73 (67%) were in first salvage therapy. Of note, the post-HSCT 100-day survival probability was similar among the 3 groups, as shown in the Table. Multivariate analyses using Cox regression modelling confirmed that MRD negativity during INO treatment and no prior HSCT were associated with lower risk of mortality post-HSCT. Other prognostic factors associated with worse OS included older age, higher baseline LDH, higher last bilirubin measurement prior to HSCT, and use of thiotepa. Veno-occlusive disease post-transplant was noted in 19 of the 101 pts who received INO.

Conclusion: Administration of INO in R/R ALL pts followed with allogeneic HSCT provided the best long-term survival benefit among those who went directly to HSCT after attaining remission and had no prior HSCT.

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