Measurable Residual Disease Analysis by Flow Cytometry and Correlation With Molecular Measurable Residual Disease in Acute Promyelocytic Leukemia: A Real-World Prospective Study.

Context.—: Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia distinguished by its rapidly progressive and fatal clinical course. Measurable/minimal residual disease (MRD) monitoring is vital for the prognosis and clinical management of acute myeloid leukemia.

Objective.—: To examine the immunophenotypes of the residual leukemic cells, evaluate the performance of multiparametric flow cytometry (FCM) measuring MRD, and compare it with molecular monitoring in patients diagnosed with APL.

Design.—: Two hundred seventy-seven patients with APL were enrolled. Immunophenotypes were prospectively analyzed by a 1-tube-10-color antibody panel via FCM. MRD of APL with PML::RARα was detected by real-time quantitative polymerase chain reaction (RQ-PCR). The clinical value of MRD as an indicator of survival was also examined.

Results.—: APL showed 5 distinct patterns of residual leukemic cells, based on CD45 and side-scatter scattergram, all with CD9 positivity and a previously unrealized loss of CD117. FCM-based MRD evaluation showed a concordance rate of 87.7% with PCR. At the end of the consolidation therapy, MRD measured by both PCR and FCM could differentiate patients with longer and shorter overall survival (OS) (P = .04 and P = .03, respectively). Patients with APL variant had a shorter OS than patients with APL who harbored PML::RARα (P < .001).

Conclusions.—: CD9 is a reliable marker to differentiate residual leukemic cells from normally differentiating myeloid cells. FCM demonstrated a high comparability to PCR-MRD and an excellent performance in predicting OS, and thus could potentially be used as a routine indicator in the clinical management of patients with APL.