Measurable residual disease in adult acute myeloid leukaemia: evaluation of a multidimensional ?radar? flow cytometric plot analysis method

Measurable residual disease (MRD) monitoring in acute myeloid leukaemia (AML) is becoming increasingly important and is predominantly performed by multiparam-eter flow cytometry (MFC) or quantitative polymerase chain reactions (RT-qPCR). We investigated the use of multidimensional plots (MD-MFC) for AML MRD moni-toring in an adult cohort. AML MRD was determined using a novel MD-MFC method for 115 MRD samples. Results were correlated with traditional two-dimensional MFC (2D-MFC) and molecular methods. Using the standard cut-off of 0.1% CD45+ cells, concordance was 99/115 (p=0.332). Eighty-four of 115 were concordant using a very low reporting limit of 0.01% (p=0.216). MRD <0.1% by either method was present in 40 of 115 samples. Fifteen of 40 were MD-MFC positive and 2D-MFC negative. Of these two of 15 had a molecular MRD marker and both were positive. Molecular MRD markers were available in 36 of 115 cases. Twenty-one of 36 (58%) were concordant with MD-MFC. Eight of 36 had detectable molecular MRD only and eight of 36 had positive MD-MFC only. There was no correlation between either the MFC method and the mo-lecular results. In summary, there is good correlation be-tween MD-and 2D-MFC-MRD and no correlation between the MFC and molecular methods.