In relapsed/refractory acute myeloid leukemia (AML), the prognostic impact of complete remission (CR) and measurable residual disease (MRD) negativity is not well established. We retrospectively analyzed 141 patients with relapsed/refractory AML who received first salvage therapy and had MRD assessed by multiparameter flow cytometry at the time of response. Patients who achieved CR with full hematologic recovery as best response vs those with incomplete hematology recovery had lower cumulative incidence of relapse (P 5.01) and better relapse-free survival (P 5.004) but not overall survival (P 5.15); a similar trend was observed in patients who achieved MRD negativity vs those who were MRD positive (P 5.01, P 5.05, and P 5.21, respectively). By multivariate analysis, CR and MRD negativity were each independently associated with lower cumulative incidence of relapse (P 5.001 and P 5.003, respectively) and better relapse-free survival (P,.001 and P 5.02) but not overall survival. Patients who achieved CR with MRD negativity had the lowest rates of relapse and best survival (2-year overall survival rate, 37%), which was driven largely by lower rates of early relapse and an increased ability in this group to undergo hematopoietic stem cell transplantation (HSCT); however, post-HSCT outcomes were similar regardless of response to salvage chemotherapy. Overall, in patients with relapsed/refractory AML, CR with MRD negativity was associated with the best outcomes, supporting it as the optimal response in this setting.
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