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.


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.


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.


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).


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.

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This study was kindly supported by the Science and Technology Project of Sichuan Province of China (Grant No. 2022YFS0213, 2023NSFSC1484) and the 1•3•5 project for disciplines of excellence-Clinical Research Fund, West China Hospital, Sichuan University (Grant No. 2023HXFH034).

Competing Interests

The authors have no relevant financial interest in the products or companies described in this article.

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