Technical and Clinical Validity of Assessing Measurable Residual Disease by Multicolor Flow Cytometry in an Unselected Acute Myeloid Leukemia Patient Cohort

Context.— Following the validation of a multicolor flow cytometry (MFC) assay for measurable residual disease (MRD) in acute myeloid leukemia (AML), this study examines its clinical applicability. Objective.— To evaluate the practicality and performance of MFC-based MRD detection in AML. Design.— Prospectively assessed AML MRD MFC in unselected AML patients achieving morphologic remission with follow-up studies, molecular genetics, and survival data. Results.— Among 379 patient bone marrow samples in this cohort, an interpretable result was obtained in 359 (95%). A total of 57 of the 359 cases (16%) were positive for MRD, and the most frequently observed immunophenotype was CD34+CD117+ myeloid (n = 46; 81%), followed by CD34−/CD117+ myeloid (n = 8; 14%) and monocytic (n = 3; 5%). Of 57 MRD+ cases, 6 (11%) had no leukemia-associated immunophenotypes available, and 16 of 51 (31%) with leukemia-associated immunophenotype for comparison exhibited significant immunophenotypic drift/switch, highlighting the importance of the “deviation from normal” approach. The remaining 302 cases were MRD negative; among these, 21 (6%) displayed a preleukemic immunophenotype that was associated with persistent clonal hematopoiesis in 18 patients (86%). A positive MFC result was strongly associated with subsequent follow-up positive MRD (41 of 45 [91%] versus 14 of 240 [6%], P < .01), morphologic relapse (42 of 55 [76%] versus 48 of 301 [16%], P < .01), an inferior overall survival (12.5 months versus not reached, P < .01), and leukemia-free survival (6.5 months versus not reached, P < .01). Among MRD-negative patients, a preleukemic phenotype was associated with a shorter overall survival (P = .03), but not leukemia-free survival (P = .16). Conclusions.— Our study provides data-driven technical insights for laboratories considering MFC AML MRD implementation and offers strong evidence supporting the utility of MRD assessment by MFC in patients with AML undergoing various stages of treatment and surveillance.