Although measurable residual disease (MRD) at the time of allogeneic hematopoietic cell transplantation (allo-HCT) has been reported to be an important prognostic factor for Philadelphia chromosome (Ph)-positive acute lymphoblastic leukemia (ALL) during first complete remission (CR1), the prognostic impact of MRD is unclear during second CR (CR2). To clarify the impact of MRD for both CR1 and CR2, we analyzed data from a registry database including 1625 adult patients with Ph1 ALL who underwent first allo-HCT during either CR1 or CR2 between 2002 and 2017. Adjusted overall and leukemia-free survival rates at 4 years were 71% and 64%, respectively, for patients undergoing allo-HCT during CR1 with MRD2, 55% and 43% during CR1 with MRD1, 51% and 49% during CR2 with MRD2, and 38% and 29% during CR2 with MRD1. Although survival rates were significantly better among patients with CR1 MRD2 than among patients with CR2 MRD2, no significant difference was observed in survival rate between patients with CR1 MRD1 and CR2 MRD2. Relapse rates after 4 years were 16% in patients with CR1 MRD2, 29% in CR1 MRD1, 21% in patients with CR2 MRD2, and 46% in patients with CR2 MRD1. No significant difference was identified in relapse rate between patients with CR1 MRD2 and CR2 MRD2. CR2 MRD2 was not a significant risk factor for relapse in multivariate analysis (hazard ratio, 1.26; 95% confidence interval, 0.69-2.29; P =.45 vs CR1 MRD2). MRD at time of allo-HCT was an important risk factor in patients with Ph1 ALL during both CR1 and CR2.
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