Comparing the Results of Non-TBI Hematopoietic Stem Cell Transplantation in Pediatric Patients with Acute Lymphoblastic Leukemia (ALL) with and without CNS Involvement

(Table1). All donor sources were included: 63 matched sibling (MSD), 95 10/10 MUD, 11 9/10 MUD, 18 cord blood (CB), and 13 haploidentical (Haplo). Results: The majority of pts received myeloablative conditioning (n1⁄4170; busulfan-based n1⁄4148). Disease status at AlloSCT was: CR1 (n1⁄499), CR2 (n1⁄420), CR with incomplete count recovery or hypoplasticmarrowor CR3 (CRi; n1⁄431), and active disease (AD; n1⁄450). Thirty percent of pts received a FLT3 inhibitorbeforeAlloSCT.After amedian follow-upof27mo, the 2-year (2Y) OS and PFS rates were 43% and 41%, respectively. Relapse-related mortality was the main cause of death (68%). Remission and FLT3 status at the time of AlloSCT were significantly associated with PFS. Compared to CR1 pts, PFS was not different inCR2 [HR1.5, p1⁄40.3], but itwasworse inCRi (HR3.9, p 4 [HR 1.6, p1⁄40.05], and unrelated donor source [HR 1.6, p1⁄40.05]. No difference in PFS was found between Haplo and MSD donor sources (HR1⁄40.9, p1⁄40.9). No significant association was identified by age, conditioning intensity or use of a FLT3 inhibitor prior to transplant. Post-transplant FLT3 status was available for 105 of 190 evaluable pts by day 30. Among them, 7ptshaddetectable FLT3PCR and5/7 pts (71%) relapsed. Conclusion: Morphologic remission and FLT3 PCR status at the time of transplant are key predictors of relapse risk in pts with FLT3+ AML. Patients who achieved a morphologic CR with an undetectable FLT3 by PCR at the time of SCT had the best outcomes and should undergo an AlloSCTwithout delay. Although the experience is limited, Haplo transplants had similar outcomes to MSD transplants. Prospective clinical trials with FLT3 inhibitors post-transplant are warranted at least for pts with AD or persistent FLT3+ on PCR at transplant.