The impact of cell heterogeneity and immunophenotypic changes on monitoring minimal residual disease in acute myeloid leukemia.Neoplasma. 2006; 53(6):500-6.N
Monitoring of minimal residual disease (MRD) becomes increasingly important for the more accurate stratification of the therapy in acute leukemia. The purpose of this study was to characterize in detail the phenotypes of heterogeneous population in various AML subtypes and to identify the leukemia associated aberrant phenotype (LAP) in individual patients with AML for precise investigation of MRD. The impact of heterogeneity of pathological populations, the effectiveness of location AML blasts on CD45/SSC dot plots in AML patients during follow-up and phenotype changes on MRD monitoring were evaluated in the second step. Bone marrow samples from 63 patients with AML were analyzed at diagnosis, 33 were selected for monitoring of MRD during follow-up and 13 analyzed at relapse using a wide antibody panel in quadruple combinations by multiparameter flow cytometry. In 88% of AML patients at least one LAP was defined at diagnosis, two or more aberrancies coexisted in 60% of them. The total number of LAPs identified by application of various combinations of antibodies was 112 (mean = 2.04 LAP/patient) and the median percentage of blasts carrying the LAP was 53.57%. In half of the patients, we were able to detect the presence of at least two subpopulations, which not always shared the same aberrancy. Although AML cells often have light scattering properties similar to those of normal (myeloid and B-lymphoid precursors, basophiles etc.) in a fraction of cases we found also very useful the location on CD45/SSC dot plots for MRD discrimination. In 13 patients relapse occurred and although we found in 69% changes of phenotype when comparing diagnosis and the first relapse, at least one LAP was constant in 92%. According to our observations, in majority of patients with AML monitoring of MRD by multiparameter flow cytometry is feasible although in some cases could present some specific difficulties owing to their immunophenotypic heterogeneity, similarity with other cell subpopulations or shifts at relapse. In conclusion, investigation of MRD should be based on the phenotypic characteristics of each subpopulation even if it is present in low frequencies.