Measurable residual disease (MRD) is an established prognostic factor after induction chemotherapy in acute myeloid leukaemia patients. Over the past decades, molecular and flow cytometry-based assays have been optimized to provide highly specific and sensitive MRD assessment that is clinically validated. Flow cytometry is an accessible technique available in most clinical diagnostic laboratories worldwide and has the advantage of being applicable in approximately 90% of patients. Here, the essential aspects of flow cytometry-based MRD assessment are discussed, focusing on the identification of leukaemic cells using leukaemia associated immunophenotypes. Analysis, detection limits of the assay, reporting of results and current clinical applications are also reviewed. Additionally, limitations of the assay will be discussed, including the future perspective of flow cytometry-based MRD assessment.

Acute lymphoblastic leukaemia (ALL) is the most common cancer in childhood but shows a very low frequency in adults. Even in the genomics era, multiparametric flow cytometry is still critical for ALL diagnosis and management. At diagnosis, it determines the proper therapeutic approach through blast characterization and lineage assignment. During treatment, it is an essential tool for response to therapy monitoring through minimal/measurable residual disease detection. Additionally, multiparametric flow cytometry is fundamental in the even more applied immunotherapy setting, recognizing any potential switch of blast immunophenotype.