Ph+ ALL patients in first complete remission have similar survival after reduced intensity and myeloablative allogeneic transplantation: Impact of tyrosine kinase inhibitor and minimal residual disease

The efficacy of reduced intensity conditioning (RIC) allogeneic hematopoietic cell transplantation (HCT) for Ph+ acute lymphoblastic leukemia (ALL) is uncertain. We analyzed 197 adults with Ph+ ALL in first complete remission; 67 patients receiving RIC were matched with 130 receiving myeloablative conditioning (MAC) for age, donor type, and HCT year. Over 75% received pre-HCT tyrosine kinase inhibitors (TKI), mostly imatinib; 39% (RIC) and 49% (MAC) were MRD(neg) pre-HCT. At a median 4.5 years follow-up, 1-year transplant-related mortality (TRM) was lower in RIC (13%) than MAC (36%;p=0.001) while the 3-year relapse rate was 49% in RIC and 28% in MAC (p=0.058). Overall survival was similar (RIC 39% [95% CI:27–52] vs. 35% [95% CI:270–44];p=0.62). Patients MRD(pos) pre-HCT had higher risk of relapse with RIC versus MAC (HR 1.97;p=0.026). However, patients receiving pre-HCT TKI in combination with MRD negativity pre-RIC HCT had superior OS (55%) compared to a similar MRD(neg) population after MAC (33%; p=0.0042). In multivariate analysis, RIC lowered TRM (HR 0.6; p=0.057), but absence of pre-HCT TKI (HR 1.88;p=0.018), RIC (HR 1.891;p=0.054) and pre-HCT MRD(pos) (HR 1.6; p=0.070) increased relapse risk. RIC is a valid alternative strategy for Ph+ ALL patients ineligible for MAC and MRD(neg) status is preferred pre-HCT.