Factors associated with allogeneic hematopoietic stem cell transplantation (HSCT) outcomes in patients (pts) with relapsed/refractory acute lymphoblastic leukemia (R/R ALL) treated with inotuzumab ozogamicin (InO) versus (v) conventional chemotherapy (C).

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7007 Background: InO therapy in R/R ALL resulted in superior complete remission (CR)/CR with incomplete hematologic recovery (CRi) rates v C in the Phase 3 INO-VATE trial (NCT01564784; Kantarjian NEJM 2016). More InO v C pts proceeded to HSCT (41% [45/109] v 11% [12/109]; P<0.001). Factors associated with outcomes after HSCT are described. Methods: Full details have been published. Multivariate analyses (MVA) using Cox regression modeling were conducted to determine predictors of non-relapse mortality (NRM) and overall survival (OS). Results: As of 3/8/16, 108/326 pts underwent allogeneic HSCT (InO n=77; C n=31). Baseline characteristics were generally similar, except baseline platelet values were lower in InO v C pts. More InO v C pts achieved minimal residual disease negativity (MRDneg [best status]; 71% v 26%; P<0.0001). Less InO v C pts received additional therapy before HSCT (14% v 55%, P<0.0001). NRM rates were higher in InO v C pts at 1 year (yr; 36% [95% CI 26–47] v 20% [8–36]) and 2 yrs (39% [27–51] v 31% [13–51]), but relapse rates were lower (1 yr, 23% [15–33] v 29% [13–48]; 2 yrs, 33% [22–44] v 46% [24–65]). No significant difference in post-HSCT survival was detected in InO v C pts; however, visual inspection of the curve suggested the survival probability varied before and after 15 months post-HSCT (1 yr, 44% [95% CI 33–55] v 65% [44–79]; 2 yr, 39% [28–50] v 34% [15–54]). Fatal veno-occlusive disease (VOD) was observed in 5 InO pts (all during the first 100 days from the date of HSCT) and no C pts. MVA showed that conditioning regimens without dual alkylators and thiotepa were associated (2-sided; P<0.05) with lower risk of NRM and post-HSCT survival, respectively. Conclusions: Compared with C, InO permitted more pts with R/R ALL to proceed to HSCT in CR/CRi with MRDneg (best status). Despite increased NRM and fatal VOD, long-term survival was attainable in InO pts. In pts previously treated with InO, interventions to reduce NRM and improve OS after HSCT include avoiding dual alkylator conditioning regimens, especially those containing thiotepa. Funding: Pfizer Clinical trial information: NCT01564784.