Minimal Residual Disease (MRD) Evaluation by Flow Cytometry in Acute Leukemia Patients Undergoing Allogeneic Stem Cell Transplantation.

Investigation of minimal residual disease (MRD) in acute leukemias by immunophenotyping is increasingly used for disease monitoring. Most MRD studies using flow cytometry techniques have focused on patients treated with conventional chemotherapy, while information on its value in patients undergoing allogeneic transplantation is scanty. The aim of the present study is to evaluate whether or not immunophenotypical assessment of MRD could also be a valuable tool in patients undergoing allogeneic transplantation for acute leukaemia. For that purpose we have analysed the level of MRD before and after (month +3) transplantation, by multiparameter flow cytometry, in a series of 38 acute leukaemia patients (26 ALL cases -20 cases in 1st CR and 6 in 2nd CR- and 12 AML cases -all of them in 1st CR), that showed an aberrant immunophenotype at diagnosis. Although the level of MRD in the BM obtained before transplantation showed a tendency to predict RFS, differences did not reached statistical significance. By contrast, the evaluation of the BM obtained 3 months after allo-transplantation had significant prognostic value. Thus, patients with low MRD levels (<0.05% for ALL and <0.2% for AML) (n=17) had a significantly longer RFS than patients with MRD positive (median RFS: 40 vs 16 months) (p=0.001). Multivariate analysis showed that the immunological evaluation of MRD after transplantation had independent prognostic value for RFS in acute leukaemia, together with age, WBC count, and cytogenetics. Our results suggest that immunological analysis of MRD should be included in the follow-up evaluation of acute leukaemia patients undergoing allogeneic stem cell transplantation.